Sandwich-Type SERS Aptasensor Based on Aptamer-functionalized Magnetic Capture Probe and AuNPs@MIL-101 Signal Enhancement Probe for Ultrasensitive Detection of <em>Bifidobacterium bifidum</em>

Rapid and on-site detection of <em>Bifidobacterium bifidum </em><em>(</em><em>B. bifidum</em><em>)</em> throughout the food manufacturing process serves as an essential sentinel for assessing product quality and healthy potency. Herein, we introduce a sandwich-type surface-enhanced Raman scattering (SERS) aptasensor for <em>B. bifidum</em> quantification, which integrates aptamer-functionalized magnetic beads (Apt-Fe₃O₄) for target-specific capture and aptamer-modified gold nanoparticles/metal-organic framework composites (Apt-AuNPs@MIL-101) for SERS-based signal amplification. Experimental results revealed a strong linear correlation between the intensity of the characteristic Raman peak and the logarithmic of the <em>B. bifidum</em> concentrations within the range of 2.0 × 10¹ to 2.0 × 10⁶ CFU/mL, and the limit of detection was as low as 2.5 CFU/mL. In addition to superior sensitivity, the proposed approach demonstrated exceptional specificity against non-target bacterial strains, particularly in multi-strain coexistent systems. The method further demonstrated great potential in analysis of <em>B. bifidum</em> in commercial samples, showing high consistency with the results obtained from the classic qPCR method. The study established an innovative analytical platform for rapid and on-site probiotic assessment, highlighting its applicability in probiotic food products’ quality control and evaluation.