Selection of Specific DNA Aptamers for Hetero-Sandwich-Based Colorimetric Determination of Campylobacter jejuni in Food

Herein, a high-affinity single-stranded DNA aptamer (59 nt) against Campylobacter jejuni, defined as CJA1, was obtained using the whole-bacterium-based systemic evolution of ligands by exponential enrichment procedure. CJA1 was analyzed with a stable secondary structure and low dissociation constant (K_d) value of 1.37 ± 0.28 nM. The potential use of CJA1 was exemplified by the construction of a hetero-sandwich platform, in which C. jejuni was bound with a biotin-tagged CJA1 to perform a colorimetric reaction that is associated with visible color changes and detectable optical responses. Dependent upon this sensing platform, C. jejuni can be detected from 1.7 × 10¹ to 1.7 × 10⁶ colony-forming units (CFU)/mL. The limit of detection (LOD) is obtained as 10 CFU/mL in PBS. The specificity study showed that the sensing platform is easy to distinguish C. jejuni from other common pathogens. Moreover, the C. jejuni-contaminated milk samples can also be accurately probed (LOD = 13 CFU/mL) without sacrificing its assay abilities, indicating the promising prospect of CJA1 in the fields of biosensing and diagnostics.