Stability and membrane-core affinity of BM-AuNP. (a) Both bare AuNPs and BM-AuNPs are stable in 2 mM citrate storage buffer. However, in 1X PBS, bare AuNPs rapidly aggregate while BM-AuNPs remain stable. (b) A fluorescence quenching assay shows the strong affinity between the coated bacterial membrane and the gold cores. Fluorescence spectra were taken from i) FITC-thiol alone, ii) FITC-thiol mixed with BM-AuNPs, and iii) FITC-thiol mixed with bare AuNPs. The concentrations of FITC-thiol and AuNP are 1 nM and 0.025 nM (equivalent to 50 μg mL−1), respectively.