Nanotechnology-based electrochemical sensors for biomonitoring chemical exposures

Abstract

The coupling of dosimetry measurements and modeling represents a promising strategy for deciphering the relationship between chemical exposure and disease outcome. To support the development and implementation of biological monitoring programs, quantitative technologies for measuring xenobiotic exposure are needed. The development of portable nanotechnology-based electrochemical (EC) sensors has the potential to meet the needs for low cost, rapid, high-throughput, and ultrasensitive detectors for biomonitoring an array of chemical markers. Highly selective EC sensors capable of pM sensitivity, high-throughput and low sample requirements (<50 microl) are discussed. These portable analytical systems have many advantages over currently available technologies, thus potentially representing the next generation of biomonitoring analyzers. This paper highlights research focused on the development of field-deployable analytical instruments based on EC detection. Background information and a general overview of EC detection methods and integrated use of nanomaterials in the development of these sensors are provided. New developments in EC sensors using various types of screen-printed electrodes, integrated nanomaterials, and immunoassays are presented. Recent applications of EC sensors for assessing exposure to pesticides or detecting biomarkers of disease are highlighted to demonstrate the ability to monitor chemical metabolites, enzyme activity, or protein biomarkers of disease. In addition, future considerations and opportunities for advancing the use of EC platforms for dosimetric studies are discussed.

Figure 1

Diagram of the exposure-effect continuum relating exposure source with dosimetric and biological response. Figure adapted from Angerer et al. (2006).

Figure 2

Strategy for the development, validation and deployment of biological monitoring sensor platforms.

Figure 3

Stripping voltammograms, current versus applied potential, of increasing methyl-parathion (pesticide) concentration, from bottom to top, 5, 10, 20, 40, 60, 80, 100, and 200 ng mL⁻¹. The inset shows the calibration curve. (Adapted from Liu and Lin, 2005)

Figure 4

Schematic of sequential injection/electrochemical immunoassay for quantification of 3,5,6-trichloro-2-pyridinol (TCP). The computer controlled sequential-injection analysis system (MicroSIA, FIAlab Instruments Inc., WA) includes six-port selection valve for delivering sample and reagents, a thin-layer cross-flow cell (MF-1095, Bioanalytical system Inc., West Lafayette, IN) that contains a glassy carbon electrode, a Ag/AgCl reference electrode and electrochemical analyzer voltammetric detection of electroactive species (Model CHI 660, CH Instruments Inc., TX). Figure adapted from Liu et al. (2005) with permission.

Figure 5

Schematic illustrating the interaction of acetylcholine (ACh) (I), and the organophosphate chlorpyrifos-oxon (II) with the active site of acetylcholinesterase (AChE).

Figure 6

Metabolic scheme for the metabolism of chlorpyrifos and the major metabolites chlorpyrifos-oxon, trichloropyridinol (and conjugates), diethylphosphate and diethythiophosphate. Figure adapted from Timchalk et al. (2004) with permission.

Figure 7

Diagram illustrating competitive immunoassay for 3,5,6-trichloro-2-pyridinol (TCP) determination. (A) immobilization of TCP antibody-coated magnetic beads to the internal wall of reactor tube by magnet; (B) washing beads with buffer; (C) injection of sample solution containing TCP analyte and TCP-horseradish peroxidase (TCP-HRP) for competitive immunoreaction; (D) washing beads with buffer; (E) injection of the substrate solution (TMB + H₂O₂) to initiate enzymatic reaction; (F) analysis of enzymatic product by electrochemical measurement. Figure adapted from Liu et al. (2005) with permission.

Figure 8

(A, top) Typical square-wave voltammetry of increasing TCP concentration in incubation solution. From bottom to top, the concentrations of TCP are 0, 0.005, 0.01, 0.05, 0.1, 0.5, 1, 2, 8, and 10 ug L⁻¹. (B, btm) Sigmoidal calibration curve of TCP using 20 uL of TCP-Ab-MBs, 50 uL of TCP-HRP in 100 uL of sample solution, 100 uL of TMB-H₂O₂ substrate solution, reaction time of 20 min. Figure from Liu et al. (2005) with permission.

Figure 9

Solubilization and detection of quantum dot (QD) tags. Scheme of an EC sandwich immunoassay (A) using primary monoclonal anti-interleukin-1α antibody immobilized on magnetic bead and QD tagged secondary anti-interleukin-1α antibody, followed by acid solubilization of CdSe core/ZnS coated QDs and detection of cadmium ions (B) by SWV (C). Adapted from Wu et al. (2007) with permission.

Figure 10

Development of a disposable EC sandwich immunoassay for the detection of prostate specific antigen, protein biomarkers of prostate cancer. Primary monoclonal antibodies were conjugated with QD and immobilized onto a glassy fiber pad and incubated with sample to capture the antigen (A), then the QD-antibody-antigen complex was migrated (B) to a second zone containing immobilized secondary antibody for capture of tagged antigen (C), followed by drawing two insulator lines with liquid blocker (super PAP pen, D) and the addition of HCl at the second zone, solubilization of the QD and EC detection of Cd+2 ions as the ions traversed laterally to the electrode surface hidden beneath a nitrocellulose membrane (E) to produce a square-wave voltammetry signal (F). Adapted from Liu et al. 2007, with permission.

Figure 11

(A) Schematic of a disposable EC immunosensors containing a primary capture region using an immobilized QD-tagged anti-prostate antigen antibody, a secondary capture regions containing secondary antibodies. Upon treatment with 1M HCl at the secondary region, cadmium ions are released and electrophorectically migrate to a bismuth/mercury-coated screen-printed electrode beneath a nitrocellulose membrane. (B) Sample is added to the strip and the electrical pins of the strip are inserted into an electronic control box of the portable EC platform. Voltage is applied to the strip and the signal output is displayed on a PC. Figure is adapted from Liu et al. 2007 with permission.

Figure 12

Computational pharmacokinetic model simulation of 3,5,6-trichloro-2-pyridinol (TCP) in blood and saliva and chlorpyrifos in blood following a repeated (3-day) dietary exposure (12 hr/day) to 0.003 mg/kg/day (RfD). The detection limit (*) for the ELISA assay is based on the value reported by the manufacturer of the TCP rapid Assay® kit (0.25 μg/L or 1E⁻³ μmol/L). Figure adapted from Timchalk et al. (2007) with permission.