(B) Photograph of the VFA device

(B) Photograph of the VFA device. to provide a critical overview of the recent progresses in highly sensitive LFIA detection technologies, involving the exploitation of enzyme-based amplification strategies. The Chromocarb features and applications of the technologies, along with future developments and challenges, are also discussed. was developed. The assay detected the histidine-rich protein 2 of by an HRP-based colorimetric assay employing the TMB substrate. A LFIA strip was ad hoc developed using a CO2 laser cutter, so that the regions for sample addition, the detection zone and the absorbent pad were linked by microfluidic channels, to reduce reagents consumption [56]. An alternative design of the LFIA platform was also proposed by Oh et al., who described a trapLFI sensor for cortisol showing deletion and detection zones instead of the traditional T- and C-lines (Physique 1). Target-bound conjugates are captured in the detection zone, whereas conjugates not binding the targets are trapped in the deletion zone. Using Chromocarb this platform, the HRP color signals increase in the detection zone and decrease in the deletion zone depending on the concentration of the target analyte. The ratio of signals from deletion and detection zones allowed to quantify cortisol in a wide concentration range (0.01C100 ng mL?1) with high detection sensitivity (9.9 pg mL?1) [52]. Open in a separate window Physique 1 Schematic illustration of mechanism Chromocarb for the trapLFI biosensor with (a) low and (b) high concentration of cortisol, and (c) comparison of signal behavior of conventional competitive Angiotensin Acetate LFIA and trapLFI biosensor in the presence of different concentrations of cortisol (- unfavorable sample, + positive sample low concentration, +++ positive sample high concentration). Adapted from Ref. [52], Copyright (2018), with permission from The Royal Society of Chemistry. As previously mentioned, HRP is commonly used as a label for CL detection, most often employing a luminol/H2O2/enhancer enzyme substrate [57]. CL is particularly suited for the development of portable biosensors due to its inherent sensitivity and simplicity (no specific sample geometry or excitation source are required) and because the emitted light can be measured using unexpensive sensors, such as photodiodes or compact CCD and CMOS video cameras [58,59,60]. Several CL-LFIA biosensors were described in the literature [61]. Furthermore, innovative detectors such as miniaturized hydrogenated amorphous silicon photodiode arrays [62], have been used for acquiring the light signal. Such sensors represented an alternative low-cost and versatile technology for the development of portable biosensors and have been used by Zangheri et al. [63] for the quantification of serum albumin in urine. To enable widespread assay application, smartphones has been also exploited as detectors in CL-LFIA systems, allowing both acquisition of the emitted light through Chromocarb the embedded CMOS video cameras and processing of the analytical signal to provide quantitative information about the target analyte [64]. HRP was also proposed for developing EC-LFIAs systems, by exploiting its electroactive features. As an example, a vertical-flow-based LFIA was developed for the simultaneous EC and colorimetric detection of influenza H1N1 viruses (Physique 2) [65]. In this assay, after sample injection, HRP-labeled antibodies bind the H1N1 viruses forming the (HRP-Ab)-H1N1 complexes, which are then detected around the gold electrode present around the LFIA strip through an EC-impedance-based method. This EC-LFIA system provided H1N1 viruses detection down to 3.3 and 4.7 PFU mL?1 in phosphate buffer saline and saliva, respectively, thus improving by 1.5-fold the performances with respect Chromocarb to the colorimetric approach. An enzyme-based EC- LFIA system was developed for the detection of cardiac Troponin T (cTnT) [66], in which a LFIA strip was combined with display imprinted carbon electrodes. This sensor, where cTnT recognition.