Multifunctional AuAg-doping Prussian Blue-based MOF: Enhanced colorimetric catalytic activities and amplified SERS signals for bacteria discrimination and detection

New strategy of a rapid, sensitive bacteria detection is highly desirable. Constructing a dual-mode colorimetric/surface-enhanced Raman scattering (SERS) biosensor is key to obtain highly sensitive discriminating and detecting of different pathogen bacteria with high accuracy. Herein, we developed a multifunctional colorimetric catalytic nanozyme (AuAg@PB MOF) composed of AuAg-doping Prussian Blue analogue-based metal-organic framework (MOF) that fabricated by self-assembled sheet growth of Ag-etched silver-coated gold nanoparticles (Au@Ag NPs) mediated by addition of ferricyanide (K3[Fe(CN)6]). AuAg@PB MOF displays ultrahigh peroxidase-mimicking activity, enhanced colorimetric signal brightness, and notably SERS enhancement. Through optimizing its Fe-doping level, peroxidase-like activity of AuAg@PB MOF is approximately 1900-fold higher than that of horseradish peroxidase (HRP), while its 3-fold enhancement in SERS signal compared with that of gold nanoparticles (Au NPs). Integrated with nanozyme-based sandwich system that made of bacteria/4-MPBA (4-mercaptophenylboronic acid)/AuAg@PB MOF, this dual-modal biosensor achieves a highly sensitive colorimetric assay of bacteria with a lower limit of detection (6 CFU/mL), and simultaneously discriminate E. coli and S. aureus by bacterial "fingerprints" spectra. Furthermore, this proposed colorimetric assay was combined with a smartphone readout-sensing platform for determining bacteria with ultra-sensitivity (2 CFU/mL). This work exhibits a novel colorimetric nanozyme used in dual-mode colorimetric/SERS sensing of bacteria.