Rapid microcystin-LR detection using antibody-based electrochemical biosensors with a simplified calibration curve approach

Abstract

Harmful algal blooms (HABs) can release cyanotoxins such as microcystins (MCs), especially, microcystin-leucine-arginine (MC-LR) which is one of the commonest and most toxic, into our water bodies and can lead to several acute or chronic diseases such as liver diseases and respiratory irritation in humans. There is an increasing need for rapid and simple detection of MC-LR in water bodies for early warning of HABs. In this study, we developed an innovative on-site screening electrochemical impedance spectroscopy (EIS) biosensor with a simplified calibration curve that can rapidly detect blooms for early action in similar water bodies. The novel aspect of this research is that various chemical cleaning procedures and surface modifications were evaluated to improve the antibody-embedded electrochemical sensor performance. In addition, a simplified calibration curve was constructed from different water samples to reduce the need for frequent recalibration in practical applications. In this study, two distinct commercially available screen-printed carbon electrodes (SPCEs) were modified as a cost-effective substrate for MC-LR biosensing with anti-MC-LR/MC-LR/cysteamine-coating. The study showed that an appropriate cleaning procedure might minimize the sensor performance difference after each electrode modification. The biosensor showed excellent sensitivity toward MC-LR detection in lake water samples with a limit of detection (LOD) of 0.34 ngL^-1. The simplified calibration curve was developed and used to predict unknown MC-LR concentrations in several lake water samples with a relative standard deviation (RSD) of 1.0-4.4% and a recovery of 75-112%, indicating the suitability of the developed biosensor and a streamlined calibration curve for rapid MC-LR measurements for different water bodies with similar water quality. This approach can therefore reduce the need for frequent calibration efforts and can be employed as the first line of testing for MC-LR in drinking and recreational water sources, especially in emergencies.

Keywords: Antibody; Biosensor; Cyanotoxins; Harmful algal blooms (HABs); Microcystin-LR; Simplified calibration curve.

Fig. 1

Surface functionalization of the MC-LR biosensor surface and mechanism for the SPCE coated with MC-LR molecules.

Fig. 2

The effect of cleaning on SPCE Type 2 (a) acetone for 90 min, (b) ethanol for 90 min, (c) acetone for 5 min, and (d) ethanol for 5 min. The redox probe solution (50 ml) of 5 mM [Fe(CN)₆]^3-/4- in 10 mM PBS was used.

Fig. 3

The effect of cleaning on SPCE Type 4. (a) acetone for 90 min, (b) ethanol for 90 min, (c) acetone for 5 min, and (d) ethanol for 5 min. The redox probe solution (50 ml) of 5 mM [Fe(CN)₆]^3-/4- in 10 mM PBS was used.

Fig. 4

Cyclic voltammogram during the surface functionalization process of the MC-LR biosensor. (a) SPCE Type 2 with acetone cleaning for 90 min, (b) SPCE Type 2 with ethanol cleaning for 90 min, (c) SPCE Type 4 with acetone cleaning for 90 min, and (d) SPCE Type 4 with ethanol cleaning for 90 min. The redox probe solution (50 ml) of 5 mM [Fe(CN)₆]^3-/4- in 10 mM PBS was used.

Fig. 5

Nyquist plots for the surface functionalization process of the MC-LR biosensor. (a) SPCE Type 2 with acetone cleaning for 90 min, (b) SPCE Type 2 with ethanol cleaning for 90 min, (c) SPCE Type 4 with acetone cleaning for 90 min, and (d) SPCE Type 4 with ethanol for 90 min. The redox probe solution (50 ml) of 5 mM [Fe(CN)₆]^3-/4- in 10 mM PBS was used.

Fig. 6

Nyquist plots with different MC-LR concentrations. (a) SPCE Type 2 with acetone cleaning for 90 min, (b) SPCE Type 2 with ethanol cleaning for 90 min, (c) SPCE Type 4 with acetone cleaning for 90 min, and (d) SPCE Type 4 with ethanol for 90 min. The redox probe solution (50 ml) of 5 mM [Fe(CN)₆]^3-/4- in 10 mM PBS was used.

Fig. 7

Calibration curves for (a) SPCE Type 2 and (b) SPCE Type 4 between with cleaning and without cleaning.

Fig. 8

Calibration curve established for Lake A water (SPCE Type 2).

Fig. 9

Simplified calibration curves developed using the SPCE Type 4 for (a) Lake B and Lake C and (b) three different water sources.