Biomarker molecules defining

Due to the complexity of organic matter sources in estuaries and the aforementioned problems associated with making only bulk measurements to constrain them, the application of chemical biomarkers has become widespread in estuarine research (see review, Bianchi and Canuel, 2001). The term biomarker molecule has recently been defined by Meyers (2003, p. 262) as compounds that characterize certain biotic sources and that retain their source information after burial in sediments, even after some alteration. This molecular information is more specific and sensitive than bulk elemental and isotopic techniques in characterizing sources of organic matter, and further allows for identification of multiple sources (Meyers, 1997, 2003). 

The term biomarker molecule has recently been defined as compounds that characterize certain biotic sources and that retain their source information after burial in sediments, even after some alteration. The catabolic and anabolic pathways that are responsible for the formation of many of the biomarker compounds occur through an intermediary metabolism via glycolysis and the citric acid cycle. 

Briefly, BM can be classified as diagnostic biomarkers, which are molecules that help to discriminate between healthy and one or more pathological states prognostic biomarkers are molecules that follow disease evolution. Predictive biomarkers are defined as the molecules that could provide relevant information to predict response or resistance to therapy they also could be used to monitor the response, as well as, in some cases, as diagnostic and prognostic biomarkers. 

Biomarkers do not measure exposure directly, but are an indicator of absorbed dose. A biomarker of exposure is defined as a xenobiotic substance or its metabolite(s) or the product of an interaction between a xenobiotic agent and some target molecules(s) or cell(s) that is measured within a compartment of an organism and can be related to exposure. Urine, blood, nail, saliva, hair, and faeces are common media collected for biomarker measurements. Maternal biomarkers of exposure can also be measured in amniotic fluid and breast milk. These matrices can also provide a measure of exposure for children, both prenatally and postnatally. Biomarkers in first teeth have also been used to assess early childhood exposure, whereas biomarkers in meconium and cord blood have been used to assess in utero exposures. Biomarkers of genetic damage (e.g. DNA adducts) have been extensively used to assess exposure to genotoxic agents (Neri et al., 2006). 

Biomarkers (BM) are defined as a characteristic of specific biomolecules, which could be an indicator of a normal or pathological process because it is possible to easily track this molecule by quantitative and qualitative detection techniques. 

A biomarker of exposure is defined as "an exogenous substance or its metabolite(s) or the product of the interaction between a xenobiotic agent and target molecule or cell that is measured within a compartment of an organism" [1]. A marker of external exposure is simply the amount of a xenobiotic substance to which a person is subjected, whereas a marker of internal exposure is the amount of a substance absorbed into the body. Markers of internal exposure are a more accurate means of estimating exposure than are markers of external exposure and require the analysis of biological samples. 

The US National Institutes of Health defines biomarkers as molecules that can be objectively measured and evaluated as indicators of normal or disease processes and pharmacologic responses to therapeutic intervention [12]. A broader definition of biomarkers for cancer consist of any measurable or observable factors in a patient that indicate normal or disease-related biological processes or responses to therapy [13, 14]. These can include physical symptoms, mutated DNAs and RNAs, secreted proteins, cell death or proliferation, and semm concentrations of small molecules such as glucose or cholesterol. In this chapter, we focus on emerging nanoscience-based electrochemical methods to detect levels of proteins as biomarkers that can be used for detection and monitoring cancer [2, 6, 15]. 

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