# Flexible Gold-Based Electrochemical Biosensor for Highly Sensitive Detection of Saxitoxin in Water Samples

## TL;DR

A flexible, low-cost gold-based biosensor was developed to detect saxitoxin in water with high sensitivity and specificity.

## Contribution

A novel flexible electrochemical biosensor for saxitoxin detection with a 15-fold lower detection limit than WHO guidelines.

## Key findings

- The biosensor has a detection limit of 0.2 μg/L, 15 times lower than the WHO guideline.
- The device showed high specificity and functioned effectively in mineral water across pH 6.2–10.2.
- The electroactive surface area of the gold electrodes was 55% larger than the geometric area.

## Abstract

Saxitoxin (STX) is a highly potent cyanobacterial toxin,
posing
serious risks to aquatic ecosystems and human health. Conventional
methods for STX detection, such as high-performance liquid chromatography
(HPLC), mass spectrometry (MS), and enzyme-linked immunosorbent assays
(ELISA), are effective but costly, labor-intensive, and nonportable,
motivating alternative strategies. Here, we report a flexible electrochemical
biosensor fabricated via photolithography of gold electrodes on affordable
polymer-based substrates for STX detection in water samples. The electrodes
showed high mechanical stability, low charge transfer resistance,
and an electroactive surface area 55% larger than the geometric area.
Anti-STX antibodies were immobilized using a simple sodium citrate-assisted
physisorption method. The biosensor response, monitored by cyclic
voltammetry in phosphate-buffered solution with [Fe­(CN)6]3–/4– as the redox probe, displayed a concentration-dependent
current decrease upon STX exposure. The biosensor operated within
the range of 0.5–6.0 μg/L and showed a detection limit
of 0.2 μg/L, which is 15 times lower than the World Health Organization
(WHO) guideline value. The device exhibited high specificity, with
negligible responses to microcystin-LR and cylindrospermopsin, and
remained effective in mineral water samples across different pH values
(6.2–10.2). This study highlights the potential of flexible,
low-cost photolithographic sensors for practical monitoring of cyanotoxins
in water samples, paving the way for broader applications in the detection
of other environmentally relevant toxins.