Rapid and accurate detection of Cyanobacterial toxin microcystin-LR using fiber-optic long-period grating based immunosensor

TL;DR

This paper introduces a highly sensitive, label-free fiber-optic immunosensor using long-period gratings and aptamers for rapid detection of the environmental toxin microcystin-LR with a detection limit of 5 ng/mL.

Contribution

The study develops a novel fiber-optic sensor combining dual-resonance long-period gratings and aptamers for specific, real-time detection of microcystin-LR, enhancing sensitivity and stability.

Findings

Detection limit of 5 ng/mL for MC-LR.

Sensor achieves ultra-sensitive spectral response (3891.5 nm/RIU).

Real-time molecular binding confirmed by atomic force microscopy.

Abstract

In this paper we present a label-free, stable and highly sensitive fiber-optic sensor for detection of environmental toxin microcystin-LR (MC-LR). Thiolated MC-LR-targeting aptamer covalently immobilized on dual-resonance long-period fiber gratings (DR-LPFG) is used as MC-LR recognition element and the spectral response of the DR-LPFG is monitored for various concentrations of MC-LR. Sensitivity of the DR-LPFG is optimized by coating an appropriate thickness of gold layer to the fiber surface. Gold coating serves two purposes, first it locally supports a surface-Plasmon mode associated with the modified cladding modes and second it helps covalently immobilize the MC-LR targeting aptamer to the sensor surface. Monitoring both the resonance wavelengths of our ultra sensitive DR-LPFGs (3891.5 nm/RIU) we study the aptamer and MC-LR binding to the sensor surface. Real-time, efficient MC-LR molecular binding to the sensor surface is also confirmed using atomic force microscopy. The detection limit of our sensor, limited by the molecule size of MC-LR, its fractional surface coverage of the sensor, and sensor length, is 5 ng/mL, which can be further improved by increasing the fractional MC-LR coverage on the sensor surface by (i) reducing the LPFG length (ii) increasing grating strength, (iii) increasing the LPFG sensitivity by coupling to even higher order cladding modes by reducing the grating period.