Sandwich method-based sensitivity enhancement of Ω-shaped fiber optic LSPR for time-flexible bacterial detection.

The development of rapid and sensitive detection methods for pathogenic bacteria is crucial for the therapy and prevention of related diseases. However, the rapid and ultrasensitive assays are difficult to be realized simultaneously. To solve the problem, a sandwich method based on Ω-shaped fiber optic localized surface resonance (Ω-FOLSPR) was constructed, where poly adenine-tailed aptamer (PolyA-apt) and SH modified gold nanoparticles tags (AuNPs tags) were chosen as the capturing aptamer and amplifying tags, respectively. The small AuNPs were modified on the surface of fiber-optic (FO) rapidly, which saved the preparation time. Then, the PolyA-apt was modified on the AuNPs surface to capture the bacteria effectively due to its ability to adjust the density and conformation of aptamer on the AuNPs surface. Finally, the large AuNPs tags were used to generate intense signal enhancement. It is found that the sandwich method enables the unique characteristic of a time-dependent sensitivity enhancement. Specifically, the LOD of 108.0 CFU/mL and 7.4 CFU/mL was achieved with the analysis time of 10 min and 100 min, respectively. Besides, the Ω-FOLSPR sensor exhibits excellent selectivity against the other bacteria and good performance for detecting the spiked and natural samples. This sandwich method provides a time-flexible strategy due to the combination of effective signal amplification and real-time analysis for bacterial detection, displaying great potential for practical bacterial detection.