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This work describes a high-yield extracellular biosynthesis of ZnS QDs via a unique molecular mediation mechanism driven by the mixed sulfate reducing bacteria (SRB). The mixed SRB have obtained the highest ever ZnS QD biosynthesis rate of 35.0–45.0 g/(L·month). The biogenic ZnS QDs with an average crystallite size (ACS) of 6.5 nm have greater PL activity and better uniformity than that of a chemical route. Peculiar extracellular proteins (EPs) with molecular weights of approximately 65 and 14 kDa specially adhere to the ZnS QDs, which cover extraordinarily high contents of acidic amino acids (14.0 mol % Glu and 13.0 mol % Asp) and of nonpolar amino acids (12.0 mol % Ala, 11.0 mol % Gly, and 7.0 mol % Phe), for novel molecular mediation. The vast amount of negative charges in Glu and Asp guides the strong absorption between the EPs and Zn2+ via electrostatic attraction to reach a maximum absorption capacity of 745.9 mg/g within 2.0 h, motivating large and rapid nucleation as the first step of biosynthesis. Meanwhile, bridging and interlinkage occur inside the EPs or between the EPs via hydrophobic interactions dominated by the nonpolar amino acids, resulting in the formation of massive microcavities to control and restrict the growth of ZnS QDs as a template. The novel molecular mediation mechanism triggered by the peculiar EPs with an extraordinary amino acid composition and structure accounts for the high-yield biosynthesis of ZnS QDs. The mixed SRB have also successfully fabricated other metal sulfide QDs, including PbS, CuS, and CdS, through the novel molecular mediation.

Quantum-dot (QD)-labeled hydrophilic molecularly imprinted polymer (MIP) microparticles were prepared for direct and highly selective optosensing of an antibiotic drug (i.e., tetracycline (Tc)) in pure bovine/goat milks and bovine/porcine serums. "Living" CdTe QD-SiO2 composite microparticles with alkyl bromide groups on their surfaces were first obtained via the one-pot sol-gel reaction, and they were subsequently grafted with a Tc-imprinted polymer layer and poly(glyceryl monomethacrylate) brushes via the successive surface-initiated atom transfer radical polymerizations. The resulting MIP microparticles with QD labeling and hydrophilic polymer brushes could function properly in biological samples and showed obvious template-binding-induced fluorescence quenching, which make them a useful fluorescent chemosensor with limits of detection down to 0.14 μM in complex biological media. Moreover, a facile and effective approach was developed based on a newly derived equation to eliminate the false positives of the fluorescent chemosensor and provide it with wider linear detection concentration ranges in comparison with those obtained using the generally adopted Stern-Volmer equation. Furthermore, the fluorescent MIP chemosensor was also successfully applied for directly, sensitively, selectively, and accurately quantifying Tc in biological media, and the average recoveries were in the range of 95%∼105% even when several other drugs and the fluorescently interfering chlortetracycline were present in the samples.