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Droplet microfluidics is a discrete fluid manipulating platform,and concentration gradient droplets can serve as parallel micro-reactors for synthesis and screening with high throughput,low consumption and low diffusion [1].A microfluidic concentration-gradient droplet array generator (CDrAG) with parallel multi-channels was developed.The novel design combined a radial channel concentration gradient generator with droplet array generation channel designs.The approach of the concentration gradient generation was demonstrated in our previous work [2].The oil phase streams were introduced from another layer or periphery of the aqueous phase channel networks.The oil phase channels were equally distributed into many branch channels,and then connected with the terminals of the aqueous phase channels via flow-focusing junctions or T-junctions respectively.Droplets were generated at the flow-focusing (Figure 1) or T-junction structures (Figure 2) due to the shear forces.Thus the droplet arrays with gradient concentrations were formed by the droplet generators.Using the concentration gradient droplet array as parallel microreactors,33 Au/Ag ratio nanoparticles were synthesized.The absorption spectra of the Au/Ag nanoparticles shifted from the spectrum of pure gold to that of pure silver.The generated Au/Ag ratios resulted in 33 optical encoding colors,with a theoretical optical code number up to (n33-1).The CDrAG was applied to screening of lysozyme crystallization conditions.The multiple factors or multiple precipitants with various concentrations for protein crystallization could be tested on a single chip.