Quantum Dots in Bioanalytical Chemistry and Medicine by Michael Thompson;Zahra Ramezani;

Author:Michael Thompson;Zahra Ramezani;
Language: eng
Format: epub
ISBN: 9781839169571
Publisher: Lightning Source Inc. (Tier 2)
Published: 2023-10-15T00:00:00+00:00

5.3 Biosensor Design Using QDs

Biosensors are designed for sensitive, specific, fast, and accurate detection of trace (ng or fg in mL) amounts of an analyte in biological, clinical, agricultural, and environmental samples. Conventionally, they consist of a biological recognition element (generally called the bioreceptor), a transducer component that converts the recognition process to a readable signal, and an electronic system (often combined with the transducer) that amplifies the detected signal (see Figure 5.2). Biosensors can also be miniaturized, and, thanks to their outstanding features, adapted for POC uses. They are classified according to the type of transducer or the biorecognition principle. There are four types of transducers: optical, electrochemical, thermal, and piezoelectric. Catalytic biosensors and affinity-based biosensors (ABBs) are two examples of biosensor categories according to their biorecognition principles. In catalytic biosensors, the analyte converts to the product in the presence of another compound that acts as a catalyst in a chemical reaction; the analyte is recognized by an Ab, antigen, aptamer, or DNA. ABBs are referred to as immune sensors when the recognition elements are antibodies or antigens. QDs have outstanding optical and electrical properties and can be used for the immobilization of biomolecules and amplification of the signal, as mediators, electroactive species, and the detection of nanoprobes in biosensor fabrications. QDs can be utilized in biosensors with different transducers, such as electrochemical, optical, thermoelectric, etc. To our knowledge, almost all current QD-based biosensors for bacterial and viral assays are based on electrochemical and optical biosensors, with QDs acting as signal amplifiers.70,71

Two biosensor classes have been developed for use in bacterial sensing: (1) processing-based systems, which require sample processing to achieve bacterial lysis to liberate the target bacterial component and (2) processing-free systems, which target whole bacteria. Analysis of the bacterial components, DNA,72,73 RNA (e.g., rRNA),74,75 intracellular proteins such as enzymes10 and secreted exotoxins,76 indicates the presence of bacteria. The major drawback of the first system type is that it requires sample processing and extra reagents, which makes these protocols more time-consuming and costly. The direct detection of whole bacteria is much more rapid and cost-effective, which makes it a much more desirable testing method at the POC. This method is particularly desirable because the infectious dose of bacteria for many human pathogens is very low; for E. coli O157:H7, the dose has been reported to be as low as only 10 cells per gram of food or environmental sample.77 See Figure 5.3.

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