Biological monitoring (biomonitoring) has the ability to integrate total chemical exposure to assess human dosimetry (Yantasee et al., 2007a
). This includes exposure from multiple sources (i.e. air, soil, water and food residues) and multiple routes of intake (i.e. inhalation, oral and dermal). A benefit of biomonitoring is the ability to associate the internal dose of a given chemical or metabolite with a measurable effect (either tissue specific or whole body), which can then be used for risk assessment purposes (Gilbert and Sale, 2005
; Christensen, 1995
; Friberg and Elinder, 1993
). Likewise, biomonitoring can be exploited to distinguish between internal (actual) from potential exposure. As suggested by Angerer et al. (2006)
and illustrated in , the exposure-effect continuum represents a framework for assessing chemical exposures and making both risk assessment and management decisions within epidemiological studies. In this regard, it is suggested that the most meaningful interpretation of epidemiology studies could be realized by accurately assessing chemical exposure with biological effect. However, a major impediment to conducting epidemiology studies is the lack of affordable quantitative technologies that can readily measure chemical exposure markers (biomarkers) using minimally invasive biological fluids (Weis et al., 2005
). To address these limitations, inexpensive micro-analytical based sensors are needed that can accurately and precisely process small amounts of biological fluids. Ideally, these sensors can be used for parallel analyses of multiple markers or quickly adapted for detection of a broad range of biomarkers associated with chemical exposure and biological response (Liu et al., 2005
; Weis et al., 2005
). As reviewed by Weis et al. (2005)
, microsensor platforms offer great promise because they have the potential to provide rapid, accurate and quantitative detection of exposure at the level of the individual. The data generated from such devices can then be used to effectively couple environmental and personal exposure assessment in a way that enhances our ability to study the factors that affect health and disease across large populations.
Figure 1 Diagram of the exposure-effect continuum relating exposure source with dosimetric and biological response. Figure adapted from Angerer et al. (2006).
The identification and quantification of target chemicals or their metabolites in biological fluids (blood, urine, and saliva) is still a cornerstone of xenobiotic metabolism research, where the analytes represent the key biological monitoring targets (Gil and Pla, 2001
; Angerer et al., 2006
). However, the utility of a specific analyte (e,g., chemical metabolite) for quantitative biological monitoring requires an appreciation of its pharmacokinetics; that is, a concentration associated with the rate of absorption, distribution, metabolism, and/or excretion in the relevant biological matrices (Timchalk et al., 2001
). A strategy for the development, validation and deployment of a chemical biomonitoring platform is illustrated in . Key criteria include identification of markers in complex matrices, such as blood, urine or saliva, validation of sensor performance, and deployment of a user-friendly platform. Validation should not only include characteristics of instrument performance (e.g., limit of detection, limit of quantification, linear performance, reproducibility, matrix effects, etc.), but the marker(s) should have positive predictive value that link chemical exposure with adverse health effects.
Strategy for the development, validation and deployment of biological monitoring sensor platforms.
This review is focused on the development and validation of portable electrochemical sensors that incorporate nanomaterials as either a signal transducer or as an electroactive species for indirect detection of analyte. Given the sensitivity, flexibility, and miniaturization capabilities, these sensors have the potential to become the next-generation of field-deployable analytical instruments. Our intent is to: 1) provide a general overview of electrochemical (EC) terminology, detection methods and integrated use of nanomaterials in the development of EC-based microanalytical instrumentation; 2) highlight recent developments using EC sensors for biomonitoring; 3) illustrate recent applications of nanotechnology-based EC sensors for detection and quantification of biomarkers of exposure or disease; and 4) discuss future considerations and opportunities for advancing the use of EC sensors for dosimetric studies.