A microbial array chip with collagen gel spots entrapping living Escherichia coli (E. coli) DH5 alpha was applied for the screening of recombinant protein solubilities. The a-fragment of beta-galactosidase (beta Gal) was fused to the target protein, namely, maltose-binding protein (MBP), to monitor the solubility of MBP. Scanning electrochemical microscopy (SECM) was used to detect the release of p-aminophenol from E. coli cells catalyzed by intracellular Peal. Comparison of the SECM-based method with the Western blotting-based method indicated that the current response' obtained using SECM increased with an increase in the beta Gal activity and therefore; with the soluble fraction of MBP in the host cells.