Innovative approaches in bioelectronics and biosensing platforms are of upmost importance to manage emergency situations such as the COVID-19 pandemic. Considering that many biomarker quantification approaches rely on either photometric or electrochemical determination without offering very often continuous monitoring to prevent critical events in the healthcare setting, the development of advanced interfacing strategies is noteworthy to improve patient safety. Regarding acute respiratory syndrome symptoms, peripheral oxygen levels (SpO₂) tend to steadily decrease upon aggravation. Notwithstanding, both SpO₂ and heartrate (HR) tend to dynamically shift according to patient health status. In this context, we investigated the use of MAX30102 photometric biosensing module coupled to personalized ESP32-based webserver to continuously gather and process SpO₂ and HR data from users (e.g. bedridden patients). Moreover, a user-friendly graphic interface was designed and implemented to better showcase biomarker levels for medical personnel and an anatomical case was 3D printed in thermoplastic polyester (polylactic acid - PLA). Results showcased that the data retrieved from MAX30102 photometric biosensor was similar to that of a standard pulse oximeter, while ESP32 webserver was able to gather, process and graphically display data in real time both in smartphones running Android and personal computers running Windows operating systems (IOS and Linux were not tested in this report). Although ESP32 showcased limitations regarding processing power, the implemented features herein described worked soundly. In conclusion, we showcased how biomarkers such as SpO₂ and HR can be continuously monitored and wirelessly interfaced to computers and smartphones through a low-cost microcontroller such as ESP32. For future investigations, we plan on implementing advanced internet of things and artificial intelligence tools to allow the herein described device to continuously evaluate patient status and predict patient critical events.

Paper-based bipolar electrochemical (P-BPEs) assays have attracted a lot of attention due to their low preparation cost, self-pumping property of paper, being portable. The dominant reporting method in the introduced P-BPEs is electrochemiluminescence (ECL). ECL limits the infield application of this type of paper-based sensor as they need expensive photon counting compartment. Therefore, the developing of a colorimetric method instead of ECL can be a promising feature. In the present study, the electrodeposition of Prussian Blue (PB) on the paper fibers has been introduced which has been used directly as a colorimetric method for the reporting cell of P-BPE. This disposable P-BPE biosensor is used for determination of glucose. The closed bipolar electrochemical cell is fabricated on a small part of paper using a laser printing-based process for paper hydrophobization. The bipolar and driving electrodes are provided by pressing the writing pencil HB on the paper. The mechanism of sensing of glucose is oxidation of the analyte in the sensing cell using glucose oxidase followed by reduction of the produced H₂O₂ by application of an external potential (10.0 V). This causes the oxidation of K₄Fe(CN)₆ in the presence of Fe(II) ions and subsequent formation of PB particles in the reporting cell. The intensity of the blue color in the reporting cell is used as a visual and colorimetric signal that can be digitally read using a scanner of digital camera. The parameters affecting the performance of the device were optimized using experimental design and chemometrics modeling. The P-BPE represents a very wide response range that extends from 0.1 mmol.L^-1 to 4.0 mol.L^-1 in the case of hydrogen peroxide, and from 0.1 to 50 mmol.L^-1 in the case of glucose. The limit of detections for hydrogen peroxide and glucose are 4.9 μmol.L^-1 and 70 μmol.L^-1 respectively.

Methylmalonic acid (MMA) plays a vital role in metabolism and energy production. It has been studied and reported as a sensitive early indicator for mild or serious Vitamin B12 deficiency. The normal range of MMA in blood among healthy people is from 0 up to 0.40 µM. Majority of MMA research was originally focused on Vitamin B12 deficiency with this small detection range. Recently, MMA has been reported to promote tumor progression due to age-induced accumulation. It was found that MMA concentration can reach as high as 80 µM in elderly people. Therefore, MMA can be a promising biomarker for cancer diagnostics, as well as a therapeutic target for cancer treatment. Clinical determination of MMA concentration in blood is normally executed by gas chromatography mass spectroscopy (GCMS) or liquid chromatography mass spectroscopy (LCMS). However, these methods require extensive sample pre-treatment, large sample volume and skilled lab personal. They are also expensive and time-consuming. Hence, we proposed an attractive and effective strategy to detect MMA with a broad linear range by a low-cost molecularly imprinted polyaniline paper sensor. The polyaniline paper strip was fabricated by a one-step solution process using MMA as the template by molecular imprinting technology. The concentration of MMA was determined by the resistance change of the paper sensor by a portable multimeter wirelessly. A calibration curve as a function of MMA concentration in aqueous solution was acquired with a correlation coefficient of 0.968. We also demonstrated detection of the added MMA in plasma with a wide concentration range of 0 to 100 µM with a limit of detection (LOD) of 0.197 µM. This low-cost disposable paper sensor has great potential in point-of-care MMA detection for cancer prognostics and diagnostics, especially in underserved communities.

Metallic nanoparticles potentially have wide practical applications in various fields ofscience and industry. In biosensorics they usually act as catalysts (nanozymes, NZ) and/or mediators in electron transfer. In our present work we describe the development of amperometric biosensors (ABSs) based on oxidases and nanoparticles of CuCe (nCuCe). nCuCe was synthesized chemically from the correspondent salts and Na₂S as a reducing agent. nCuCe, being a very active peroxidase (PO) mimetic, was used here as a hydrogen peroxide sensing platform for oxidase-based ABSs. Using glucose oxidase (GO), alcohol oxidase (AO), methylamine oxidase (AMO), L-arginine oxidase (ArgO), and nCuCe as PO-like NZ (for GO, AO, AMO and ArgO-based ABSs) and as electro-active mediator (for laccase-based ABS), the biosensors on glucose, primary alcohols, methyl amine, L-arginine and catechol, respectively, were constructed and characterized. Enzymes were isolated from the correspondent over-producing cells according to the methods, proposed by the authors earlier. The developed mono-enzyme ABSs exhibited improved analytical characteristics in comparison with the correspondent bi-enzyme ABSs, which contained natural PO. Including electrodeposit nanoporous gold (npAu) in chemosensing layer on graphite electrode (GE), allows to additionally increase sensitivity of the constructed ABSs twice due to the increased and advanced surface. As an example, the bioelectrodes, containing laccase/GE, laccase/nCuCe/GE and laccase/nCuCe/npAu/GE had the sensitivities, respectively, 2300, 5055 and 9280 A·M⁻¹·m⁻². The proposed laccase-based ABSs were successfully tested on the samples of pharmaceuticals and food products for analysis of phenolic compounds.

An important and critical characteristic for continuous monitoring using DNA biosensor is the microfluidic design. Some of the significant functions of microfluidic structures used in DNA biosensors are sample manipulation, effective and rapid reaction and ultra-low detection limit of the analyte. This study explores different designs and parameters of microfluidic microchambers. The selection of the appropriate geometrical design and control of microfluidic parameters are highly important for the optimised performance of the biosensor. Several combinations of different shapes of microchambers are designed and assessed computationally. Flow parameters such as average velocity, pressure drop, flow rates and shear parameters are critically assessed at different cross-sections within the microchamber.

Optimised design of the microchamber is selected based on optimal rinsing, minimum flow shear, avoidance of slow zones, simple geometry and homogenous distribution of the analyte target. Steady and unsteady laminar flow simulations were performed using a commercial Computational Fluid Dynamics software. A range of different geometrical shapes were assessed using parametric studies and a design optimisation analysis. 3D printing technology was used to construct and evaluate the optimised designs in combination with experimental investigations which were carried out and the optimum design was selected and characterised.