Electrochemical sensors for the detection of lead and other toxic heavy metals: the next generation of personal exposure biomonitors

Abstract

To support the development and implementation of biological monitoring programs, we need quantitative technologies for measuring xenobiotic exposure. Microanalytical based sensors that work with complex biomatrices such as blood, urine, or saliva are being developed and validated and will improve our ability to make definitive associations between chemical exposures and disease. Among toxic metals, lead continues to be one of the most problematic. Despite considerable efforts to identify and eliminate Pb exposure sources, this metal remains a significant health concern, particularly for young children. Ongoing research focuses on the development of portable metal analyzers that have many advantages over current available technologies, thus potentially representing the next generation of toxic metal analyzers. In this article, we highlight the development and validation of two classes of metal analyzers for the voltammetric detection of Pb, including: a) an analyzer based on flow injection analysis and anodic stripping voltammetry at a mercury-film electrode, and b) Hg-free metal analyzers employing adsorptive stripping voltammetry and novel nanostructure materials that include the self-assembled monolayers on mesoporous supports and carbon nanotubes. These sensors have been optimized to detect Pb in urine, blood, and saliva as accurately as the state-of-the-art inductively coupled plasma-mass spectrometry with high reproducibility, and sensitivity allows. These improved and portable analytical sensor platforms will facilitate our ability to conduct biological monitoring programs to understand the relationship between chemical exposure assessment and disease outcomes.

Keywords: biomonitoring; dosimetry technology; electrochemical sensors; exposure assessment; lead (Pb).

Figure 1

Various electrochemical sensors for metal detection: (A) carbon paste working electrode for batch detection, (B) screen-printed electrode, (C) electrochemical cell, and (D) schematic of a portable metal analyzer [10.6 in (length) × 9.7 in (width) × 6.9 in (diameter)]. Abbreviations: A, auxillary; R, reference; W, working. Reproduced from Yantasee et al. (2005b), with permission of Elsevier.

Figure 2

Pb signals as a function of Pb concentrations in solution without blood and with blood samples prepared by spiking Pb before and after proteins are removed; inset shows the corresponding voltammograms of Pb in 10-vol% blood sample. Reproduced from Yantasee et al. (2007), with permission of Springer.

Figure 3

Pb signals as a function of Pb concentrations in samples with 0, 10, and 50 vol% of urine; inset shows the corresponding Pb voltammograms in 50%-urine samples. Reproduced from Yantasee et al. (2007), with permission of Springer.

Figure 4

Voltammetric responses of Cd and Pb at the microanalyzer, measured in single component Pb and Cd solutions and a multicomponent Pb/Cd solution. Operating conditions are described in Table 1; inset shows the corresponding voltammograms.

Figure 5

Voltammetric responses of Cu at the microanalyzer. Operating conditions are described in Table 1; inset shows the voltammograms of 5, 10, 20, 50, and 100 μg/L of Cu. y = 0.16x; R² = 1.00

Figure 6

A hybrid of (A) self-assembled monolayer and (B) ordered mesoporous silica resulting in (C) SAMMS structure with (D) three differing organic moieties as the monolayers. SiO₂, silicon dioxide.

Figure 7

A Pb calibration curve at a 10 wt% AcPhos–SAMMS screen-printed sensor after 5-min preconcentration. Inset (A) shows the corresponding Pb voltammograms; inset (B) shows the simultaneous detection of 90 ppb Cd, 18 ppb Pb, and 18 ppb Cu. y = 0.034x; R² = 0.999. Reproduced from Yantasee et al. (2005a), with permission of Elsevier.

Figure 8

Calibration curve of Pb in samples containing 25 vol% urine measured after 5 min preconcentration at a IDAA–SAMMS–CNT paste electrode; inset shows the corresponding Pb voltammograms. y = 0.316x; R² = 0.998.