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Heart failure (HF) is a serious and debilitating cardiovascular disease responsible for high mortality and morbidity rates worldwide, as well as expensive healthcare costs. In HF, there is an increase in circulating concentrations of cardiac biomarkers such as N-terminal B-type natriuretic peptide (NT-proBNP), which can be used for its diagnosis and prognosis. Biosensors have emerged as an appealing alternative to conventional methods of detection, being capable of providing a quick response and allowing detection at point of care. Tilted fiber Bragg gratings (TFBGs) present a high sensitivity to refractive index (RI) variations occurring in the surrounding medium and hence were employed in this work to develop a biosensor for NT-proBNP detection. Two immunosensors were exploited based on a bare TFBG and a gold coated TFBG (Au-TFBG), and, in both cases, distinct spectral demodulation methods were studied to evaluate the sensing performance. The NT-proBNP detection was carried out using the immunosensors properly biofunctionalized, in the 0.01-1000 ng/mL concentration range. The best performance results were obtained by computing the lower envelope of the spectra and following its variations for both bare and Au-coated TFBGs, with the latter exhibiting a lower limit of detection of 0.19 ng/mL. Moreover, a control test was done for each immunosensor to test the specificity. The findings reached in the present work highlight the great diversity of spectral demodulation methods and their impact on the sensing performance, having to be considered upon comparison between TFBG-based biosensors.
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