Notes

Loop mediated isothermal amplification (LAMP) is a technique to sensitively and selectively amplify nucleic acid at a constant temperature in a simpler manner than PCR [10]. Because LAMP eliminates the need for an advanced thermocycler, this technique can be deployed in field applications where access to a stable power supply is limited

To address this technical issue, multiple integrated sensors have been developed to allow rapid POC diagnosis for TB to be performed and analyzed on electronic devices

On a similar note, an electrochemical immunosensor based on the principle of sandwich immunoassay used with a portable potentiostat device was establish to detect MPT64, a marker for Mtb proliferation

As such, they offer minor value as POC technology in their current state. In this work, we have integrated LAMP with an electrochemical (EC) biosensor that has recently gained momentum as an alternative technology for rapid point-of-care nucleic acid detection. This is due to an instrumental footprint that can be engineered for portability

EC operates on the principle that redox molecules can be used to enhance the electrochemical signals of biological agents, which are usually not highly electroactive. Hoechst 33,258 (C25H37Cl3N6O6) is one of the most popular redox molecules given its rapid quenching upon binding to the minor grooves of double-stranded (ds) DNA, resulting in a dramatic reduction of the current to a level that can be measured by simple voltammetric methods . Such quenching properties means EC can be useful for nucleic acid detection, as
demonstrated in PCR-EC and LAMP-EC for the identification of single nucleotide polymorphisms (SNPs) in humans and livestock, respectively.

Miniaturization of EC biosensors requires an enabling electrode to make portable EC platforms match the performance of other advanced sensors. In the past, a simple paper-based electrode (ePAD) was reported for Mtb DNA detection via impedance measurement

Graphene electrodes can be fabricated by a number of scalable techniques, such as drop coating, inkjet printing, spray coating, and screen-printing. The last method is remarkably popular by virtue of its simplicity, high production rate, high reproducibility and cost-effectiveness Owing to its value in scalable fabrication, screen-printing has been exploited to prepare screen-printed carbon electrodes (SPCEs) for electrochemical sensing. Although various surface and bulk modification methods have been used to further improve the property of SPCEs the technique that shows the highest promise and practicality is directly mixing graphene into the carbon paste or replacing it entirely. The resulting screen-printed graphene electrodes (SPGEs) exhibit greater electron transfer rates and larger effective surface areas for electrochemical analysis compared to SPCEs . Using SPGE for voltammetry analysis has enabled portable electrochemical sensors to be more practical and accessible in broader applications . In this work, an integrated point-of-care platform was developed by analyzing LAMP products by an electrochemical device (LAMP-EC) that operates on a system combining SPGEs, Hoechst 33,258 (H33258) redox probe and a portable potentiostat (referred to as the mini-potentiostat in this manuscript) for the rapid detection of Mtb. The working principle of the LAMP-EC is summarized in