Biosensors
Biosensors
The biosensors can be defined as devices made by an element of biological recognition (antibodies, enzymes, proteins, nucleic acids, organelles and cells), with the propertie to recognize and interact with the analyte of interests. From this interaction results the changing of physicochemical properties that are detected and measured by the transducer, which converts the information into a measurable signal. The definition is illustrated at the Figure 1.
Figure 1: Schematic configuration of a biosensor [1]
To ensure a good functionality, in general the sensors may present some of the characteristics presented at the Figure 2:
Figure 2: General characteristics of the biosensors
The uses of this interdisciplinary technology give us the chance to monitoring the environmental field, healthly, animal, agriculture, livestock, among others. Most part of the transduction forms can be classified in methods of electrochemistry detection, thermometrics, optics, etc. The electrochemistry sensors, which one electrode is using as an element of transduction, it’s highlight due to his large linear range of reply, good sensibility, trust and reproducibility. In this context, the thin films production using the Layer by Layer – LbL technique [2] to modify electrodes, has been allowed the fabrication of new systems/devices set, providing advantages like: low cost, easy handling and synergyc interactions between the different compounds of film [3].
The optical biosensors based in immunoassay of lateral flux (LFIA), also called essay Immunochromatographic, are an attractive tool [4-6] and an example of method that have been used in the detection of proteins, toxins, among others. The most popular application is the pregnancy test that was based in the detection of HCG na urina [5, 7]. The LFIA has recently generate scientific and industrial interest allowing diagnostics in situ, quick and easy handling, which the qualitative analysis can be taken observing the results with naked eye [4, 6].
The LFIA consists generally of 4 different parts: the sample pad, the conjugation pad, the detection pad and the absorbent pad (Figure 3). The sample pad, made of cellulose, has the role to accept the sample, filter out the sample from impurities and stock the “tampão de ensaio”. The conjugation pad, gerally made by fiberglass is used to stock the maskers (the nanoparticles of gold – AuNP – for example, quantum dots, etc). He accepts the conjugated and keep him stable, liberating him when the essay it’s been executed. In the detection pad, made by nitrocellulose, the reagents of capture are immobilized and the signal is developed. Finally the absorbent pad, which is usually made of cellulose has the role to remove all liquid added in the strip, keeping him in the region of the absorbent pad during the essay [5, 8].
Figure 3: Illustrative scheme of the LFIA method
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[4] Nagatani, N.; Tanaka, R.; Yuhi, T.; Endo, T.; Kerman, K.; Takamura, Y.; Tamiya, E.; Gold nanoparticle-based novel enhancement method for the development of highly sensitive immunochromatographic test strips. Sci. Technol. Adv. Mater., v.7, p. 270-275. 2006.
[5] Wong, R. C.; Tse, H. Y. Lateral Flow Immunoassay. Springer, DOI 10.1007/978-1-59745-240-3, 224 pg. 2009.
[6] Anfossi, L.; Baggiani, C.; Giovannoli, C.; D’Arco,G.; Giraudi, G. Lateral-flow immunoassays for mycotoxins and phycotoxins: a review. Anal. Bioanal. Chem., v. 405, p. 467-480. 2013.
[7] De la Escosura-Muñiz, A.; Parolo, C.; Merkoçi, A. Immunosensing using nanoparticles. Materials Today, v. 13, p. 24–34. 2010.
[8] Parolo, C.; Merkoci, A. Paper-based nanobiosensors for diagnostics. Chem. Soc. Rev., v. 42, p. 450-457. 2013.
