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Biosensors
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Antibody-antigen bioreceptors
editAn antibody is a protein that has high specificity to certain specific structures. They are produced by the immune system to identify and bind to specific antigens so that an immune response can occur. The interaction between an antigen and its antibody is analogous to a lock and key fit.[1] As such, only the specific analyte of interest, the antigen, fits into the antibody binding site.[1]
Nucleic acid bioreceptors
editNucleic acid bioreceptors (or sometimes referred to as genosensors) rely on the specific Watson-Crick base pairing for recognition of DNA.[1] If the base sequence of a DNA molecules of interest is known, then the complementary sequence (called a probe) can be synthesized and labelled.[1] The detection scheme begins with unwinding of the double-stranded DNA into single strands, adding the probe, and then annealing the strands.[1] If the DNA molecule of interest is present, the labelled probe will hybridize to its complementary sequence and produce a measurable signal.[1]
Enzymatic bioreceptors
editEnzymes are used as bioreceptors due to their specific binding capabilities as well as their catalytic activity.[1] The catalytic activity provided by enzymes allows for much lower limits of detection than with common binding techniques. All enzymes are proteins (except for a small group of catalytic ribonucleic acid molecules).[1] Some enzymes require cofactors (such as inorganic ions) or coenzymes for their catalytic activity.[1] The catalytic activity of enzymes depends on the native protein conformation.[1] As such, it is important to ensure that the enzyme is not denatured, dissociated into its subunits, or broken down into its component amino acids in order to preserve its catalytic activity.[1]
Cellular bioreceptors
editCellular bioreceptors are based on biorecognition by an entire cell, microorganism, or a specific cellular component that is capable of specific binding to an analyte.[1] Cellular bioreceptors usually have very low detection limits due to signal amplification.[1] Cellular bioreceptors rely on the uptake of certain chemicals into the microorganism for digestion and transport.[1] Subsequently, cell metabolism (e.g.: growth inhibition, cell viability, substrate uptake), cellular respiration, bacterial bioluminescence, or analyte localization can be used for analyte recognition and evaluation.[1]
Biomimetic receptors
editA biomimetic receptor is an artificial receptor fabricated and designed to mimic a bioreceptor.[1] Fabrication methods of biomimetic receptors include genetically engineered molecules, artificial membrane fabrication, and molecular imprinting.[1] Using genetic engineering techniques, hybrid bioreceptors can be created to contain peptide sequences from multiple sources for customized bioreceptor activity.[1] Artificial membranes incorporating molecules into lipid matrices can also be used to tune bioreceptor activity.[1] Molecular imprinting refers to the mixing of analyte molecules with monomers and crosslinkers.[1] After polymerization, the hard polymer is ground into powder and the analyte molecules are extracted with organic solvents to remove them from the polymer network.[1] The resulting polymer has molecular holes that act as complementary binding sites to the analyte of interest.[1]
References
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