The Application of Biomedical Engineering Techniques to the Diagnosis and Management of Tropical Diseases: A Review <s> Biosensors <s> A polypeptide chain formed by recombinant antigens, cytoplasmic repetitive antigen (CRA) and flagellar repetitive antigen (FRA) (CF-Chimera) of Trypanosoma cruzi , was adsorbed on gold and platinum electrodes and investigated by electrochemical impedance spectroscopy on phosphate buffer saline solutions (PBS) containing a redox couple. It was found that the adsorption is strongly sensitive to the oxide layer on the electrode surface. In the majority of the experiments the antigens retained their activity as observed through their interaction with sera from chronic chagasic patients. The results expressed in terms of the charge transfer resistance across the interface, indicate the viability of using the impedance methodology for the development of a biosensor for serological diagnosis of Chagas’ disease. # 2003 Elsevier B.V. All rights reserved. <s> BIB001 </s> The Application of Biomedical Engineering Techniques to the Diagnosis and Management of Tropical Diseases: A Review <s> Biosensors <s> Bioelectrodes to detect immunoglobulin G (IgG) antibodies occurring in sera of patients suffering from American trypanosomiasis were assembled. The device consisted of a gold electrode modified with a thiol sensitized with parasite proteins. The assemblage was accomplished by adsorbing IgG antibodies from confirmed infected patients followed by adsorption of anti-human IgG labeled with a redox enzyme. The appliance was used as a working electrode in a three-electrode cell containing a soluble charge-transfer mediator, also behaving as enzyme cosubstrate. The method is based on the measurement of the catalytic current after addition of the enzyme substrate, occurring when a positive serum is used to build up the biosensor. The discrimination efficiency between positive and negative sera was 100% for the samples studied. A 0.9525 correlation coefficient was obtained for results acquired by using this approach and one commercial diagnostic kit. The reproducibility, evaluated by the percentage coefficient of variation, varied between 7 and 20%. The sensitivity was 12.4 ng mL(-1) IgG, which is in the same order as that obtained with the commercial kit. Stability of the device was studied for a 7-day period and the results showed no significant change (p = 0.218). Leishmaniasic sera showed cross-reactivity when total parasite homogenate was used as antigen. <s> BIB002 </s> The Application of Biomedical Engineering Techniques to the Diagnosis and Management of Tropical Diseases: A Review <s> Biosensors <s> Clinical immunoassays often display suitable sensitivity but some lack of specificity or vice versa. As a trade-off between specificity improvement and sensitivity loss, biosensors were designed to perform indirect immunoassays with amperometric detection using tailor-made chimeric receptors to react with the analyte, specific anti-Trypanosoma cruzi immunoglobulin G (IgG). Recombinant chimeras were designed to favor their oriented covalent attachment. This allows the chimeras to properly expose their epitopes, to efficiently capture the analyte, and to withstand severe chemical treatment to reuse the biosensors. By further binding the secondary antibody, horseradish peroxidase-labeled anti-human IgG, in the presence of the soluble mediator and the enzyme substrate, a current that increased with the analyte concentration was measured. Biosensors using the chimeric constructions showed 100% specificity with samples that had revealed false-positive results when using other bioreceptors. A protein bearing a poly-Lys chain and thioredoxin as directing elements displayed the highest signal-to-noise ratio (P<0.05). The limit of detection was 62 ng ml⁻¹, which is eight times lower than that obtained with a currently used commercial Chagas enzyme-linked immunosorbent assay (ELISA) kit. Reusability of the biosensor was assessed. The signal was approximately 80% of the original one after performing 10 consecutive determinations. <s> BIB003
A Chagas disease biosensor has been reported by Diniz et al. BIB001 . It had gold and platinum electrodes that were coated with an oxide layer and recombinant antigens (cytoplasmic repetitive antigen and flagellar repetitive antigen for Chagas), and dipped in patient's serum. The study showed that complex impedance increases much faster when the electrodes are dipped in Chagas positive serum, compared to a slower increase in impedance when dipped in Chagas negative serum. In a similar study by Ribone et al. BIB002 , a biosensor utilizing gold electrodes was constructed. Similar to the Chagas ELISA method, the electrode is covered with Trypanosome cruzi antigen that reacts with patients' anti-Trypanosome cruzi IgG. A classic enzyme label using horseradish peroxidase conjugated with anti-human IgG was applied. However, instead of using the typical optical detection method, a potential of less than 0.1 V was applied and electrode current was measured. An increase in current indicates an increase in IgG antibody. In a separate study by Belluzo et al. BIB003 , the same biosensor was improvised with custom made chimeric receptors that react with the IgG antibody. The biosensor was shown to achieve 100% specificity while attaining increased sensitivity with a detection limit that is eight times lower compared to commercially available ELISA kits.