Optical fiber SPR biosensor with frequency multiplexing compensated laser heterodyne feedback for ultrasensitive detection of fluoroquinolones

The widespread usage and discharge of fluoroquinolones (FQs) have caused negative environmental consequences that can threaten human health. The development of ultrasensitive and simple devices for detection of various FQs is an important requirement. Here, we proposed a novel optical fiber surface plasmon resonance biosensor to achieve the ultrasensitive detection of FQs, in which the frequency-shifted light returned to the laser resonator and stimulated laser heterodyne feedback interferometry to amplify the intensity changes caused by the refractive index (RI) variations. In addition, we further presented a quasi-common path frequency multiplexing compensation method to compensate for the noise of the developed biosensor, resulting in a RI resolution of 1.06 × 10⁻⁶ RIU. Besides, the gold nanorods were used to generate localized surface plasmon resonance to further amplify the signal to achieve the ultrasensitive detection. A variety of FQs were detected with ultra-low detection limits, including enrofloxacin (0.61 ng/L), ciprofloxacin (0.54 ng/L), norfloxacin (0.31 ng/L), pefloxacin (0.32 ng/L), and sarafloxacin hydrochloride (0.97 ng/L). With the advantages of high sensitivity, compact size, and remote operation capability, the developed biosensor holds the promise of detecting other antibiotics with universality in hard-to-reach spaces, thus having the potential to demonstrate a promising approach to environmental monitoring.