Printing porous polymer filmWe initiated our approach by employing a 405 nm light projector, which consisted of a 405 nm light source and a digital micromirror device (DMD) chip, integrated into a digital light processing 3D printer, as depicted in Fig. 1a. The DMD-based maskless lithography facilitated the projection of a customized pattern from the personal computer onto the printing platform in the form of blue light, thereby inducing localized polymerization of the prepolymer solution that is placed between the platform and the substrate. When a liquid mixture, composed of hydroxyethyl methacrylate (HEMA), ethylene glycol dimethacrylate (EDMA) as a cross-linking agent, 2,2-dimethoxy-2-phenyl acetophenone as a photoinitiator, along with cyclohexanol and 1-decanol as porogens, was used as the prepolymer solution for printing, it underwent phase separation during the light-induced cross-linking process, resulting in the formation of a porous structure within the printed polymer film. Polymerization occurred exclusively in the exposed regions, while leaving the unexposed areas as liquid for subsequent removal after printing, which enables the precise patterning of porous polymer films with specific designs on the substrate. To enhance resolution in printed polymer patterns, especially with extended exposure times, we introduced Sudan 1, a light absorber, and 4-methoxyphenol, a polymerization inhibitor, to the monomer mixture. After inserting a spacer (a 6 μm thick polyimide film was used in this study) between the substrate and printing platform to uniformly control the thickness of the prepolymer liquid film, we achieved diverse porous polymer films with varying porosity at specific positions through adjustment of exposure times in various areas (Fig. 1b and Supplementary Fig. 1). This allows the creation of gradient porosity and transmittance in the printed patterns by manipulating regional light exposure based on grayscale values from computer software-designed target patterns (Fig. 1c, Supplementary Figs. 2 and 3). Importantly, this printing approach was universally adaptable to different substrates, demonstrating success in printing porous polymer patterns on methacrylate-pre-treated rigid glass or flexible polyethylene terephthalate (PET) films (Fig. 1d). The covalent bonding between the polymer film and the substrate ensured firm adhesion even after repeated bending (Supplementary Fig. 4).Fig. 1: Patterned polymer chip printing.a Schematic representation of chip printing using a DMD-based maskless lithography system. The designed pattern on the PC side is projected onto the platform in the form of 405 nm blue light, inducing localized polymerization of the prepolymer solution. b Photograph and water contact angle measurements of the printed porous polymer with varying exposure times. Scale bar: 500 μm. An SEM image of the printed polymer film (60 s exposure) with porous morphology is inserted. Scale bar: 1 μm. c Optical photograph of a printed landscape pattern with gradient porosity. Scale bar: 5 mm. d Printed polymer pattern on a flexible substrate. Scale bar: 5 mm. e Schematic representation of border-part and island-part polymer printing, along with their corresponding printed polymers featuring different pattern sizes. Scale bar: 500 μm. f A printed polymer line pattern with a width of 8 μm. Scale bar: 100 μm. g Fluorescence intensity analysis of two stripe arrays, demonstrating printing uniformity. Scale bar: 500 μm.Having validated the feasibility of this printing technology, we delved into its resolution and uniformity aspects. Figure 1e illustrates polymer films with two different feature-size array configurations, referred to as the border-part and island-part. While it has been widely reported that reducing the distance between structures can be more challenging than reducing the feature sizes50, our printing experiments yielded impressive results for both configurations, achieving a remarkable resolution of 80 μm (equivalent to the single pixel size of the DMD chip we utilized). By employing an alternative DMD projector system with smaller pixel sizes, we successfully printed a polymer pattern with 8 μm features, as depicted in Fig. 1f. The uniformity of the porous polymer film fabricated using these different equipment setups was verified through fluorescence intensity analysis of the printed patterns (Fig. 1g and Supplementary Fig. 5). This analysis underscores the versatility of this printing method, showcasing its adaptability across various devices and configurations.To enable direct ambient condition printing, we conducted an investigation into the printability of small features within maskless lithography, a process often hindered by the proximity effect and oxygen inhibition. For example, in the border-part polymer array, reducing the internal square space while maintaining the border width mitigates the impact of dissolved oxygen on polymerization, resulting in reduced exposure times (Supplementary Fig. 6). Even when projecting border-part patterns at an 80 μm distance, no noticeable proximity effect was observed. This confirms the effective elimination of radical diffusion, which typically causes the proximity effect, through the addition of polymerization inhibitors Sudan 1 and 4-methoxyphenol (Supplementary Figs. 7, 8). On the contrary, in the island-part polymer array, diminishing the polymer square size while maintaining a constant blank spacing amplifies the impact of oxygen, resulting in a prolonged induction period and subsequently extending the required exposure time (Supplementary Fig. 6). Remarkably, when the polymer square island size reaches 80 μm, successful printing with well-defined edges necessitates an inert gas atmosphere. The shorter exposure time observed under this condition provides additional evidence of oxygen’s role in photo-polymerization. Encouragingly, an approach to manage photoinitiator radical diffusion and alleviate inhibitory effects has been proposed through the reduction of exposure time while simultaneously increasing light intensity51. As shown in our study in Fig. 1f, polymer printing tasks featuring small details within ambient conditions were facilely manipulated with the aid of an intensified light source. In this way, we have achieved the creation of high-resolution patterned porous polymer structures on diverse substrates using a DMD-based projector, streamlining the customization of regionally functionalized polymer chips.Dual post-chemical modification of printed chipsWhen porous polymer patterns are applied to the substrate through printing, the chip gains versatile dual post-modification capabilities. To exemplify this, we present a practical demonstration featuring printed polymer patterns on a transparent glass substrate.Firstly, within the porous polymer structure, the intrinsic hydroxyl groups of HEMA monomers act as anchoring sites for subsequent chemical transformations (Fig. 2a). An esterification reaction was conducted in the presence of triethylamine, involving perfluorooctanoyl chloride and the printed polymer borders, to illustrate this possibility. Energy dispersive X-ray (EDX) mapping revealed a uniform distribution of fluorine element (F) exclusively on the polymer’s surface, indicating the successful attachment of fluorinated chains to the porous matrix. Notably, this small-molecule reaction, as evidenced by SEM images (Fig. 2b and Supplementary Fig. 9), preserved the porosity and surface roughness of the patterned polymer, both crucial for achieving superhydrophobicity in the printed polymer patterns. Water contact angle (WCA) measurements on various polymer films printed with varying exposure times and subsequently modified with perfluorooctanoyl chloride verified the realization of a superhydrophobic state (Fig. 2c). A state of superhydrophobicity could be reliably attained by controlling the exposure time within the range of 32 to 65 s. Excessively short or excessively long exposure times proved ineffective in rendering the printed polymer films superhydrophobic, primarily because they failed to generate the necessary surface roughness. Remarkably, linear abrasion tests demonstrated the superior mechanical durability of the fluorinated, polymer-patterned polymer films (exposure time: 60 s) (Supplementary Fig. 10). They maintained their superhydrophobic characteristics even after enduring 14 cycles of abrasion on sandpaper with a roughness of 5000 grit under a pressure of 2770 Pa.Fig. 2: Dual post-chemical modification of printed chips.a Schematic diagram illustrating modifications on the printed porous polymer pattern via esterification or photo-grafting. b SEM image of the perfluorooctanoyl chloride-modified polymer pattern. Scale bar in zoom-in image: 500 nm. EDX mapping indicates the uniform distribution of the F (blue) element on the polymer pattern. c WCA and sliding angle measurements of the perfluorooctanoyl chloride-modified porous polymer prepared with varying exposure times. Values in (c) represent the mean, and the error bars represent the SD of the three measured values of the sample. d Organic solvents with different surface tensions confined within the perfluorooctyl acrylate-grafted polymer rings. e Schematic diagram of photo-induced regional modification on glass substrate via thiol-ene click reaction or photo-grafting. f WCA variation of the glass substrate after modification with different thiols or (meth)acrylates. Values in (f) represent the mean, and the error bars represent the SD of the three measured values of the sample. PFDT 1H,1H,2H,2H-perfluorodecanethiol, HDFDMA 2-(Perfluorooctyl)ethyl methacrylate, TG 1-thioglycerin, MTAC Methacrylatoethyl trimethyl ammonium chloride. g Schematic of a droplet sliding along the patterned hydrophilic pathway on a glass substrate. h Photographs of the droplet sliding on the substrate at a tilting angle of 60°, before and after MTAC modification. Scale bar: 5 mm. i Schematic diagram of the DMF droplet sliding on the regional fluorinated glass substrate. j Photographs of the DMF droplet sliding on the substrate at a tilting angle of 60°, before and after PFDT modification. Scale bar: 5 mm.In order to further reduce the surface energy of the printed polymer pattern and enhance its liquid repellency, we explored leveraging the residual alkene groups within the polymer matrix as initiation sites for spatial polymerization of a fluorine-containing monomers. Upon reutilizing the DMD-based projector to regionally irradiate the polymer film wetted with the perfluorohexylethyl methacrylate monomer solution, we observed that the post-modified porous polymer began to exhibit enhanced resistance to organic solvent infiltration (Supplementary Fig. 11). Even when subjected to dichloromethane with a surface tension as low as 26.5 mN m−1 52, the printed oleophobic polymer rings continued to display liquid repellency (Fig. 2d). This undoubtedly advances the potential applications of polymer printing chips in the realm of handling organic droplets.The anchor groups on glass, specifically 3-(methacryloyloxy) propyltrimethoxysilane, previously mentioned for enhancing adhesion with the polymer film, also maintained their reactivity for subsequent chemical modifications using photo-induced techniques such as thiol-alkene reactions or free radical polymerization (Fig. 2e). Alterations in WCAs on the glass substrate confirmed successful grafting of hydrophobic or hydrophilic thiols or (meth)acrylates (Fig. 2f). Maskless photolithography on the glass substrate enabled targeted chemical modification as well. As demonstrated in Fig. 2g, on a glass chip with a “U-shaped” polymer film, we initiated methacrylatoethyl trimethyl ammonium chloride polymerization on the glass, creating a curved and hydrophilic pathway. When tilted, water droplets followed this path, infiltrating the printed porous polymer film (Fig. 2h). Similarly, organic N,N-dimethylformamide (DMF) droplets slid along the 1H,1H,2H,2H-perfluoro-1-decanethiol-modified pathway with dewetting ability (Fig. 2i, j).Stacked liquid layers on printed chipsPatterned chip surfaces are anticipated to function as microchemical reactors for multi-step chemical processes within these droplets. This necessitates the capacity to manage diverse liquid layers, including both aqueous and organic solutions, on this platform. To achieve this, we harnessed precise control over porous polymer printing sites and subsequent post-chemical modifications to create polymer patterns with varying shapes and chemical properties for the confinement of various liquid layers.We initiated the process by printing a polymer array with a capsule shape, created by combining left and right segments (Fig. 3a, b). Polymer fluorination was performed after printing the left half, while the blank glass region underwent 1H,1H,2H,2H-perfluoro-1-decanethiol treatment to impart dewettability to these regions in the end. When lifted from an aqueous solution with methylene blue staining, differential wettability caused the right side to absorb the solution, while leaving the left superhydrophobic side of the capsules dry. This selective absorption allowed for the subsequent absorption of the low surface energy solvent and segregation from the aqueous phase on the right (Fig. 3c). Employing polymer films with varying wettabilities, including oleophobic, superhydrophobic, and hydrophilic patterns, proved highly effective in containing and separating immiscible aqueous and oil droplets.Fig. 3: Stacked liquid layers on printed chips.a Sequential printing and selective chemical modification of a polymer array with capsule-shaped structures. b Optical images of polymer printing at various stages. Scale bar: 1 mm. c The superhydrophilic polymer (right half) infiltrated with blue-dyed water and the superhydrophobic polymer (left half) subsequent infiltrated with toluene stained with Oil Red O. Scale bar: 2 mm. d A printed chip designed for multi-phase liquid stacking systems. Scale bar: 5 mm. e Schematic diagram of constructing vertical multi-layer-stacked droplet via bottom-up injection sequence. f Photographs of the water and toluene stacking process on the chip, confined by the printed polymer frame. Scale bar: 5 mm. g Microscope images displaying the unchanged solid-liquid contact line on the chip’s surface after toluene infiltration. Scale bar: 2.5 mm. h Schematic diagram of constructing vertical multi-layer-stacked droplet via top-down injection sequence. i Photographs illustrating the vertical stacking process of water, toluene, and DCM. Scale bar: 5 mm. Microscope images at the bottom depict chip changes as each phase is introduced. Scale bar: 2.5 mm. Colored dots mark the chip-liquid contact lines, showing their relative positions in (j). k Schematic representation of the lateral multi-layer-stacked droplet construction process. l Photographs showing the lateral stacking process of water, 1,3-dibromopropane, and octyl acetate. Scale bar: 5 mm. m A combination of vertical and lateral stacking. A saturated aqueous sodium bromide solution (ρ = 1.5 g ml−1) was injected underneath the hexadecane layer. Scale bar: 5 mm. n The stability test of the lateral stacking system. Photographs show the laterally placed water and hexadecane liquid rings, in which the n-hexadecane outer ring has dye dissolved (ring ii), after standing for 0 h and 24 h. Scale bar: 5 mm. Absorbance curves in (o) indicate no cross-contamination between the hexadecane liquid rings after standing for 24 h.Capitalizing on this property, we designed and printed polymer films with concentric circular structures on a glass substrate with a central circular groove, post-chemically fluorinated to act as a droplet-based microreactor (Fig. 3d and Supplementary Fig. 12). Utilizing the superhydrophobic polymer and hydrophilic glass patterned circular ring structure, a blue-dyed aqueous solution (ρ = 1 g mL−1) was confined between the superhydrophobic polymer rings, forming a water ring with an arched cross-section. Upon introducing toluene (ρ = 0.9 g mL−1) on top of aqueous layer, the lower-surface-tension toluene layer was entrapped by the superhydrophobic layer, floating on the water due to density differences, resulting in the formation of vertically stacked liquid layers (Fig. 3e, f). Notably, the solid-liquid contact line on the chip surface remained unaltered after toluene infiltration, indicating that the water ring’s effective ability to restrict toluene both horizontally and vertically (Fig. 3g).When conducting multi-phase reactions on the chip surface, it may become necessary to introduce a new phase of reactant solution either above or below the existing layer(s). This requires the reaction platform to support both vertical bottom-up and top-down injection sequences for liquid addition. In the top-down injection approach (Fig. 3h), the aqueous phase with higher density was injected beneath the pre-existing toluene layer, followed by the subsequent injection of denser dichloromethane (ρ = 1.33 g mL−1). Surface patterning efficiently guided the toluene-wetting line to the superhydrophobic film’s edge as water and dichloromethane were injected, resulting in the formation of a stable, stacked three-liquid layer structure (Fig. 3i). A side view of the droplet system shown in Supplementary Fig. 13 revealed the layered encapsulation. In this droplet construction mode, the polymer film consistently demonstrated the liquid-locking effect, evident from the solid-liquid contact line’s variation on the chip surface (Fig. 3j).In the vertically stacked configuration of the aforementioned liquid layers, their arrangement depended solely on individual densities. To broaden the options for various liquid phases, we have developed a lateral stacking system, enabling liquid lateral injection to form stacks in various arrangements (Fig. 3k). Using a patterned glass substrate with concentric circular structures of superhydrophobic polymer and hydrophilic glass, two pairs of concentric liquid rings, namely 1,3-dibromopropane (ρ = 1.98 g mL−1) and water, octyl acetate (ρ = 0.87 g mL−1) and water, were introduced laterally from the center towards the outer edge. With gravity support from the glass substrate and the polymer film’s locking effect on liquids, the lateral multiphase liquid layers allowed for flexible adjustment of the arrangement sequence, thus liberating them from density constraints (Fig. 3l, Supplementary Figs. 14, 15). Moreover, the lateral stack can be expanded by extending the circles of the liquid phase outward, opening up possibilities for constructing complex multi-phase systems. When necessary, vertical stacking and lateral stacking methods can be combined (Fig. 3m). Crucially, absorbance and fluorescence analysis of the patterned lateral liquid rings on the chip demonstrated the effective hindrance of lateral diffusion of the liquid rings, thereby preventing cross-contamination between the spaced-apart layers (Fig. 3n, o and Supplementary Fig. 16). Since the water rings on this chip are designed to be affixed to the glass region, rather than on polymer films which are prone to hydrolysis, the formed aqueous droplets remain stable for more than 3 weeks, even when the chip is exposed to acidic (pH = 1) or alkaline (pH = 12) conditions (Supplementary Fig. 17). While droplet evaporation poses a concern with certain liquids, employing specific measures can effectively mitigate or prevent it (Supplementary Fig. 18). This enhanced corrosion resistance, coupled with the convenient generation of multi-layer-stacked droplet microarrays (Supplementary Fig. 19), opens up new possibilities for exploring applications where this chip can be effectively used as a chemical microreactor.In-situ monitoring of chemical processes in dropletsOur initial examination of the droplet system as a microreactor involved the use of droplets containing vertically stacked double liquid layers to extract fluorescent dyes from both phases (Fig. 4a). After depositing an aqueous solution containing amphiphilic fluorescent dyes (dye 1) onto a glass chip with a central groove, followed by the injection of toluene on top, a layered liquid-liquid interface in the droplet was established to facilitate mass transfer. To enhance the transfer process, we introduced a magnetic stirrer bar into the groove of the chip, inducing controlled oscillations in the layer-stacked droplet. As expected, localized stirring was crucial for expediting the extractions, allowing the completion of the extraction process in 1 h under condition of 400 rpm (Fig. 4b, c). Notably, these oscillations occurred without compromising the integrity of the entire stack of liquid layers. The effectiveness of utilizing droplets with lateral stacked liquid rings for extraction across various phases was also validated (Supplementary Fig. 20). The introduction of controlled oscillation in this system can be achieved by gently shaking the chip containing liquid rings at an optimal speed.Fig. 4: Real-time monitoring of chemical processes in multi-layer-stacked droplets.a Configuration of an in-situ extraction microreactor based on multi-layer-stacked droplets. The setup involves introducing an aqueous phase containing dye(s) into the chip, overlaying it with a toluene liquid layer, and sealing the system with a lid to prevent toluene volatilization. Oscillations in the droplet are introduced through magnetic stirring. Scale bar: 10 mm. b Fluorescence microscopy images in the FITC channel (center ring) of the aqueous phase containing dye 1, alongside photographs of the toluene phase (outer ring) during the extraction process, with and without stirring. Time points in the droplet system are presented in a donut shape. c Fluorescence intensity curves of the aqueous phase over time, corresponding to the two extraction conditions in (b). d Real-time monitoring of color changes in the aqueous phase (center ring) and toluene phase (outer ring) at various time points during the extraction reaction. The corresponding color distribution is displayed on the right. Initial concentrations of dye 1 and methylene blue dye 2 in the aqueous phase were 0.2 mg mL−1 and 1.5 mg mL−1, respectively. Scale bar: 2 mm. e Absorbance curves of the collected toluene phase and aqueous phase before and after extraction, with optical images of the solutions inserted. Scale bar: 5 mm. f Real-time spectroscopic monitoring by integrating chip-confined droplets with a commercial microplate reader, with the detected information of the liquid layers displayed in real-time on a computer. Scale bar: 20 mm. g Setup for the real-time spectroscopic monitoring of Rhodamine B extraction from the aqueous solution to the n-hexadecane phase in a double-layer-stacked droplet. Scale bar: 20 mm. h Absorbance curve for in-situ detection of the n-hexadecane phase during the extraction reaction, with the trend of the absorption peak at 558 nm displayed.Compared to conventional bulk chemical reactions, chemical operations within these droplets offer notable benefits to monitor reactions within the nearly flat, stationary droplets on the chip in real time. To illustrate this, we initially employed optical microscopy to observe the selective extraction process within the droplets in situ. After dissolving both methylene blue (dye 1) and amphiphilic molecule dye 2 in the aqueous phase, forming a vertically stacked structure with toluene layer, we observed that the amphiphilic dye 2 molecules migrated from the aqueous layer to the toluene layer, while ionic methylene blue molecules remained in the aqueous phase. Real-time monitoring of the extraction process was enabled through colorimetric analysis, which tracked the evolution in color between the aqueous and toluene phases at different time points (Fig. 4d). Detection of absorbance from both liquid layers confirmed the completion of the extraction process, in line with the observed cessation of color change within the liquid layers (Fig. 4e).When dealing with chemical processes featuring low concentrations or no observable color changes within the droplets, optical microscopy proved insufficient. We, therefore, integrated chip printing, droplet handling, and a commercial microplate reader for droplet-based chemical investigations to expand the scope of real-time monitoring (Fig. 4f). For instance, after dissolving Rhodamine B in an alkaline solution with pH 13, the aqueous phase was covered with n-hexadecane to form a stacked liquid layer for extraction. Once the chip was placed in the detection chamber of the microplate reader and the light test probe was positioned beneath the hexadecane liquid layer, real-time scanning of absorbance in the liquid phase during the extraction process was initiated (Fig. 4g). The results, as shown in Fig. 4h, captured the complete evolution of hexadecane liquid phase absorbance over time. As the introduction of the commercial microplate reader enabled in-situ quantitative analysis in this study, it becomes apparent that the customization and integration of printed polymer chips, commercial detection devices, and operational software hold the potential to deliver a more convenient and precise in-situ monitoring solution for chemical reactions and processes within droplets.Chemical transformation in dropletsIn this section, we harnessed patterned printed chips to construct a droplet system with multiple liquid layers, enabling the execution of a chemical synthesis. To illustrate the transfer and purification of intermediate products across different liquid phases in the synthesis, we selected a set of classic chemical transformations as a demonstration (Fig. 5a). While the reactions can be conducted in batch or flow-chemistry setups or even in a centrifuge-driven liquid stack, our compact droplet system presents advantages arising from its user-friendly droplet manipulation, adjustable reaction parameters and the open design of the entire setup.Fig. 5: Chemical synthesis in three-layer-stacked droplets.a Chemical scheme illustrating a synthesis of dimethyl 1,4-phenylenediacrylate in distinct liquid phases. b Schematic representation of the same chemical synthesis within a three-layer-stacked droplet microreactor on the chip. c Absorbance curve tracking the evolution of reaction (i) and the phase transfer of the resulting product, providing confirmation of successful completion. The inset displays the absorption peak at 268 nm as a function of time. d Absorbance curve monitoring the final product P1 and P2 in the 1,3-dibromopropane phase, confirming the completion of reaction (ii), phase transfer of I2’, and reaction (iii). The inset shows the trend of the absorption peak at 302 nm as a function of time. e 1H NMR spectra of the purified P1 product from reaction (iii), comparing the results from bulk reaction (top) and droplet synthesis (bottom). f 1H NMR spectroscopy of mixed raw products obtained from the droplet microreactor at two different feeding ratios of reactant 1 and 3 (1:1 and 2:1), resulting in varying ratios of final products P1 and P2.First, we established an octyl acetate layer containing triphenylphosphine alongside an aqueous phase, resulting in vertically stacked liquid layers, as shown in Fig. 5b. The straightforward introduction of bromoacetic methyl ester into the octyl acetate layer initiated the in-situ generation of an alkyltriphenylphosphonium salt, which gradually transitioned into the aqueous phase under oscillation (Supplementary Fig. 21). The completion of the first-stage reaction was confirmed by monitoring the absorbance in the aqueous phase, particularly observing the absorption peak at 268 nm (Fig. 5c). Subsequently, we injected 1,3-dibromopropane containing terephthalaldehyde into the aqueous phase while removing the octyl acetate to enhance the yield. This emphasizes how the openness of this multi-phase droplet system simplifies droplet manipulation during and after reactions, especially when employing a machine-assisted liquid dispenser for both liquid addition and withdrawal. Upon introducing potassium carbonate into the aqueous phase, the alkyltriphenylphosphonium salt, formed in the initial step, precipitated as an insoluble solid (ylide). Subsequently, the ylide migrated into the 1,3-dibromopropane phase under the influence of gravity, where it underwent a reaction with terephthalaldehyde, resulting in the formation of alkene products (Fig. 5d). The interaction among diverse liquid layers within the droplets simplifies the generation and purification processes of the intermediate product, as evident.We then compared the products generated through bulk reactions with those collected from the layer-stacked droplets. The resulting 1H NMR spectra displayed identical peak positions for both products, confirming the successful completion of this chemical synthesis in the droplets with a comparable yield (Fig. 5e). Theoretically, this reaction should yield two products, monoester P1 and diester P2. Upon reducing the feeding ratio of reactant 3, a comparison of the integrated area of peaks at 6.6 ppm (corresponding to the absorption peak of P1) and 6.5 ppm in the 1H NMR spectra revealed the appearance of diester P2, with its proportion gradually increasing in the reaction products (Fig. 5f and Supplementary Fig. 22). The effectiveness of the multiphase droplet system in facilitating control over chemical synthesis has been demonstrated.Machine-assisted high-throughput reactions in droplet arraysReactions in droplets on flat substrates provide distinct advantages, including minimal reagent usage, high-throughput processing, easy droplet manipulation, and the capability for real-time monitoring of reactions within the droplets through instrument combinations. These characteristics render this system highly beneficial for serving as a miniaturized platform for autonomous synthesis, both homogeneous and heterogeneous, especially conducive to conducting gradient reactions or combinatorial chemistry in an array. To progress towards machine-assisted autonomous synthesis, we integrated an automatic liquid dispenser into our liquid-reaction system to create isolated or stacked liquid layers, demonstrating its efficiency in swiftly conducting parallel reactions on our platform (Fig. 6a).Fig. 6: Machine-assisted droplet manipulation.a Schematic illustration demonstrating the application of an automatic liquid dispenser to generate liquid droplets, both organic and aqueous, for subsequent reactions. b Droplet weight measurements demonstrating the liquid dispenser’s ability to dispense droplets uniformly and quantitatively. c Precise assignment of droplets at designated locations while maintaining their shape using a printed polymer frame on the platform. Scale bar: 5 mm. d Machine-assisted arrangement of droplets into stable stacked-layer structures under different injection sequences. Scale bars: 5 mm. e Formation of individual droplets first on the patterned platform, followed by manipulation to facilitate contact. The coalescence of separated DMF and water droplets is shown on the right. Scale bars: 5 mm. f Manipulation of droplet environment through controlled contact between droplets. The color change of resazurin according to the varied droplet pH is demonstrated. Scale bar: 5 mm. g Demonstration of the liquid dispenser’s capacity to generate droplets with diverse concentrations. Scale bar: 5 mm.After confirming the automatic liquid dispenser’s ability to uniformly and quantitatively dispense droplets at designated locations (Fig. 6b and Supplementary Fig. 23), we observed that the printed polymer frame effectively maintained the shape of the droplets, which was beneficial for both organic and aqueous solutions (Fig. 6c). This is crucial for forming stacked liquid layers. Regardless of the injection sequence, whether in a top-down, bottom-up, or lateral manner, as anticipated, the automatic liquid dispenser successfully arranged the droplets into stable stacked-layer structures within the multi-phase system formed by water and octyl acetate (Fig. 6d and Supplementary Movie 1).The method of forming individual droplets first and then manipulating them to make contact, rather than using a dispenser to print droplets with direct contact between them, appears to be more effective for controlling multiple droplets simultaneously. To validate this approach, we designed the shape of the printed polymer frame to create a center-encircling pattern (Fig. 6e). Under normal conditions, the droplets in each spot remain stable and do not make contact with each other. Upon applying specific interference, however, such as droplet squeezing, to two or more adjacent droplets, controlled contact between them occurs. If the contacting droplets are miscible, they coalesce to form a new droplet, as depicted in Fig. 6e with DMF and water droplets. Alternatively, they form a stable stacked-layer structure afterward if the contacting droplets are immiscible (Supplementary Fig. 24).This controlled contact between droplets offers the opportunity to manipulate reaction conditions or the order of reactant addition. As a simple demonstration, we printed a droplet of acidic solution containing Resazurin (pH = 3) on the center spot, which exhibited a bright yellow color at the given pH. Upon merging the central droplet with surrounding dispensed droplets (either HCl solution or NaOH solution), the color of the droplets turned first to blue and then to pink as the pH of the environment changed (Fig. 6f). Coupled with our successful utilization of an automatic liquid dispenser to dispense droplets with gradient concentrations (Fig. 6g), this establishes the theoretical feasibility for the subsequent conduction of high-throughput droplet reactions on our printed platform.The high-throughput droplet system’s reaction model focuses on verifying the catalytic reduction of resazurin by hydroxylamine using gold nanoparticles (AuNP), with varying reactant concentrations. Initially, we created a polymer frame array with 8 rows and 11 columns on a quartz substrate measuring 100 × 75 mm. Each frame was divided into three independent sub-units: the center zone and the surrounding two zones (Fig. 7a). With the aid of automatic liquid dispenser, we sequentially distributed AuNP dispersion, resazurin solution, and NH2OH solution at different concentrations into these sub-units (Fig. 7b and Supplementary Movie 2). This droplet-loaded substrate was tailored to fit into a custom-made sandwiching aligner (Supplementary Fig. 25), enabling us to utilize another quartz cover with superhydrophobic frames to establish a sealed observation environment (Supplementary Fig. 26). When closed, the aligner sandwiched the droplet-loaded chip and the cover, facilitating precise point-to-point squeezing of the three individual droplets to coalesce them into one for all the droplet sub-units in a single step. This coalescence of reactant droplets initiated all reactions simultaneously. Upon transferring the aligner to the microplate reader equipment, programmed oscillation and point-by-point detection ensured thorough mixing of components in each droplet and effective collection of absorbance change information over time in each unit (Supplementary Figs. 27, 28). Following 8 h of reaction, each droplet exhibited an intensity of characteristic absorption from the product corresponding to the reactant concentration (Fig. 7c, d). Thus far, this systematic reaction has validated three key aspects: machine-assisted loading of different reaction components separately, initiation of all parallel reactions in a single step, and programmed machine oscillation and real-time monitoring of each reaction unit during the reaction process.Fig. 7: Machine-assisted high-throughput screening of chemical transformations in droplets.a Schematic illustrating the combination of an automatic liquid dispenser and a microplate reader to conduct parallel reactions in droplets. Arrayed droplets containing reactants are dispensed onto the sub-unit zones with the aid of the liquid dispenser. For the parallel initiation of all reactions, the cover chip, printed with superhydrophobic frames, is fixed on the upper surface of the sandwiching aligner, making contact with the droplet-loaded substrate on the lower surface in a sandwich configuration for squeezing the individual sub-unit droplets to coalesce them into one. Oscillation and point-by-point detection are carried out automatically by the microplate reader. b Optical image showing the automatic dispensing of reactant liquids onto each sub-unit zone. Scale bars: 5 mm. c Optical images of the arrayed droplets during the reaction, showing distinct color changes in individual droplet reaction units. Scale bars: 5 mm. d Automatic point-by-point detection of the intensity of characteristic absorption from the product, revealing the chemical transformations in each droplet unit.
