Immunofunctionalisation of gold transducers for bacterial detection by physisorption

Functionalisation of the sensing surface is a key factor in immunosensor fabrication as it allows target-selective capture and prevents nonspecific adsorption of undesired components. Gold immunofunctionalisation using self-assembled monolayers (SAM) has been widely exploited to this end for the detection of small targets. However, we recently demonstrated that this strategy fails when detecting whole bacteria cells (Baldrich et al., Anal Bioanal Chem 390:1557-1562, 2008). We now investigate different physisorption-based alternatives using E. coli as the target organism. Our results demonstrate that physisorption generates the appropriate substrate for the specific detection of bacteria on gold surfaces, providing detection limits down to 10(5) cells mL(-1) in an ELISA-type colorimetric assay. Additionally, surface coverage is highly reproducible when assayed by impedance spectroscopy and the inter- and intra-assay coefficients of variation are below 10-15% in all cases. These surfaces were stable, retained functionality and did not suffer from significant biomolecule desorption after 10 days storage in PBS at 37 degrees C, hence confirming physisorption as a cheap, simple and efficient strategy for the detection of bacteria.