Highly selective sensor for the detection of Hg2+ ions using homocysteine functionalised quartz crystal microbalance with cross-linked pyridinedicarboxylic acid

Abstract

This study reports an insightful portable vector network analyser (VNA)-based measurement technique for quick and selective detection of Hg²⁺ ions in nanomolar (nM) range using homocysteine (HCys)-functionalised quartz-crystal-microbalance (QCM) with cross-linked-pyridinedicarboxylic acid (PDCA). The excessive exposure to mercury can cause damage to many human organs, such as the brain, lungs, stomach, and kidneys, etc. Hence, the authors have proposed a portable experimental platform capable of achieving the detection in 20-30 min with a limit of detection (LOD) 0.1 ppb (0.498 nM) and a better dynamic range (0.498 nM-6.74 mM), which perfectly describes its excellent performance over other reported techniques. The detection time for various laboratory-based techniques is generally 12-24 h. The proposed method used the benefits of thin-film, nanoparticles (NPs), and QCM-based technology to overcome the limitation of NPs-based technique and have LOD of 0.1 ppb (0.1 μg/l) for selective Hg²⁺ ions detection which is many times less than the World Health Organization limit of 6 μg/l. The main advantage of the proposed QCM-based platform is its portability, excellent repeatability, millilitre sample volume requirement, and easy process flow, which makes it suitable as an early warning system for selective detection of mercury ions without any costly measuring instruments.

Fig. 1

Process flow of biosensor for selective Hg²⁺ ions detection using QCM sensor

Fig. 2

VNA‐based experimental platform for microfluidic application for selective Hg²⁺ ions detection using QCM sensor

Fig. 3

QCM‐1 Sensor analysis after PDCA coating (a) Change in frequency of QCM‐1 sensor after a thin‐film coating of HCys‐PDCA on the top Au surface, (b) Surface topography after PDCA coating for selective Hg²⁺ detection

Fig. 4

QCM‐1 Sensor analysis after Hg²⁺ exposer (a) Change in frequency of QCM‐1 sensor with $\mathrm{HgC}{\mathrm{l}}_2$ concentration in the range of 0.001–1355 ppm after a thin‐film coating of HCys‐PDCA on the top Au surface (sensor area) after a thin‐film coating of HCys‐PDCA on the top Au surface, (b) Surface topography after Hg²⁺ detection

Fig. 5

QCM‐2 Sensor analysis after PDCA coating (a) Change in frequency of QCM‐2 sensor after a thin‐film coating of HCys‐PDCA on the top Au surface, (b) Surface topography after PDCA coating for selective Hg²⁺ detection

Fig. 6

QCM‐2 Sensor analysis after Hg²⁺ exposer (a) Change in frequency of QCM‐2 sensor with $\mathrm{HgC}{\mathrm{l}}_2$ concentration in the range of 0.001–1355 ppm after a thin‐film coating of HCys‐PDCA on the top Au surface (sensor area) after a thin‐film coating of HCys‐PDCA on the top Au surface, (b) Surface topography after Hg²⁺ detection

Fig. 7

Change in frequency of QCM‐3 sensor for detection of Hg^{2 +} ions using VNA‐based portable experimental platform with a lower range of concentration 0.1–2.71 ppm after a thin‐film coating of HCys‐PDCA on the top Au surface

Fig. 8

Change in frequency of QCM‐3 sensor for detection of Hg²⁺ ions using VNA‐based portable experimental platform with the concentration of 2.71–27.1 ppm after a thin‐film coating of HCys‐PDCA on the top Au surface

Fig. 9

Stability of QCM device with respect to time (a) 0.1 ppb, (b) Complete range of 0.1 ppb–27.1 ppm for selective detection of mercury ions

Fig. 10

Change in frequency ( $\mathrm{\Delta }f$ ) for QCM‐1, QCM‐2, and QCM‐3 devices

Fig. 11

Change in surface roughness and topography of QCM sensor after a thin‐film coating of HCys‐PDCA on the top Au surface (i.e. before Hg detection) (a) Two‐dimensional AFM image, (b) Two‐dimensional AFM phase image

Fig. 12

Change in surface roughness and topography of QCM sensor after Hg²⁺ ions exposer (a) Two‐dimensional AFM image, (b) Two‐dimensional AFM phase image

Fig. 13

EDX spectra for SAM of HCys‐PDCA (a) Scan area for analysis, (b) Tabular form of element detected and spectra of elements detected, (c) Colour mapping of different element detected during EDX analysis

Fig. 14

EDX spectra of QCM‐1 for SAM of HCys‐PDCA after exposer to Hg^{2 +} ions (a) Scan area for analysis and tabular form of element detected, (b) Spectra of elements detected, (c) Colour mapping of different element detected during EDX analysis

Fig. 15

EDX spectra of QCM‐2 for SAM of HCys‐PDCA after exposer to Hg²⁺ ions (a) Scan area for analysis and tabular form of element detected, (b) Spectra of elements detected, (c) Colour mapping of different element detected during EDX analysis