Reagent-Free Lactate Detection Using Prussian Blue and Electropolymerized-Molecularly Imprinted Polymers-Based Electrochemical Biosensors

Sweat lactate, a promising biomarker for assessing physical performance and health conditions, calls for noninvasive, convenient, and affordable detection methods. This study leverages molecularly imprinted polymers (MIPs) as a synthetic biorecognition element for lactate detection due to their affordability and high stability. Traditional MIPs-based electrochemical sensors often require external redox probes such as ferricyanide/ferrocyanide in the solution to signal the binding between analytes and MIPs, which restricts their applicability. To address this, our study introduces an innovative approach utilizing a layer of Prussian blue (PB) nanoparticles as the internal redox probe on screen-printed carbon electrodes (SPCE), followed by a layer of electropolymerized MIP (eMIP) for molecular recognition, enabling reagent-free lactate detection. The real-time growth of eMIP and the processes of template elution and lactate rebinding were examined and validated using electrochemical surface plasmon resonance (EC-SPR) spectroscopy. The sensor's performance was thoroughly investigated using Differential Pulsed Voltammetry (DPV) and Electrochemical Impedance Spectroscopy (EIS) with samples spiked in 0.1 M KCl solution and artificial sweat. The developed sensors demonstrated a fast and selective response to lactate, detecting concentrations from 1 to 35 mM with a Limit of Detection (LOD) of 0.20 mM, defined by a signal-to-noise ratio of 3 in the DPV measurements. They also exhibited excellent reproducibility, reusability, and a shelf life of up to 10 months under ambient conditions. These eMIP/PB/SPCE-based lactate sensors show considerable potential as point-of-care (POC) devices for sweat lactate detection, and the technology could be adapted for reagent-free detection of a broad spectrum of molecules.

Recent Advances in Wearable Biosensors for Non-Invasive Detection of Human Lactate

Lactate, a crucial product of the anaerobic metabolism of carbohydrates in the human body, is of enormous significance in the diagnosis and treatment of diseases and scientific exercise management. The level of lactate in the bio-fluid is a crucial health indicator because it is related to diseases, such as hypoxia, metabolic disorders, renal failure, heart failure, and respiratory failure. For critically ill patients and those who need to regularly control lactate levels, it is vital to develop a non-invasive wearable sensor to detect lactate levels in matrices other than blood. Due to its high sensitivity, high selectivity, low detection limit, simplicity of use, and ability to identify target molecules in the presence of interfering chemicals, biosensing is a potential analytical approach for lactate detection that has received increasing attention. Various types of wearable lactate biosensors are reviewed in this paper, along with their preparation, key properties, and commonly used flexible substrate materials including polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), paper, and textiles. Key performance indicators, including sensitivity, linear detection range, and detection limit, are also compared. The challenges for future development are also summarized, along with some recommendations for the future development of lactate biosensors.

Dual-Color Fluorescent Hydrogel Microspheres Combined with Smartphones for Visual Detection of Lactate

Since it is difficult for human eyes to distinguish between two identical colors with only <15% variation in brightness, mono-color fluorescent hydrogel microspheres have some limitations in the detection of lactate. Herein, we prepared novel dual-color fluorescent hydrogel microspheres, which can achieve hue transformation. Microspheres were prepared by introducing a fluorescent nanoparticle as the reference signal while CdTe QDs were used as the response signal. We used smartphones with image processing software to collect and analyze data. In this way, the signal of lactate was converted to RGB (red, green, and blue) values, which can be quantitatively read. Within 10 to 1500 μM, the R/G values of the microspheres had a linear relationship with the logarithm of the lactate concentration. Moreover, color cards for lactate detection were prepared, from which the color change and concentration of lactate could be easily read by the naked eye. It is worth mentioning that this method was successfully applied to screen patients with hyperlactatemia.

Investigation of Flexible Arrayed Lactate Biosensor Based on Copper Doped Zinc Oxide Films Modified by Iron-Platinum Nanoparticles

Potentiometric biosensors based on flexible arrayed silver paste electrode and copper-doped zinc oxide sensing film modified by iron-platinum nanoparticles (FePt NPs) are designed and manufactured to detect lactate in human. The sensing film is made of copper-doped zinc oxide (CZO) by a radio frequency (RF) sputtering system, and then modified by iron-platinum nanoparticles (FePt NPs). The surface morphology of copper-doped zinc oxide (CZO) is analyzed by scanning electron microscope (SEM). FePt NPs are analyzed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The average sensitivity, response time, and interference effect of the lactate biosensors are analyzed by voltage-time (V-T) measurement system. The electrochemical impedance is analyzed by electrochemical impedance spectroscopy (EIS). The average sensitivity and linearity over the concentration range 0.2-5 mM are 25.32 mV/mM and 0.977 mV/mM, respectively. The response time of the lactate biosensor is 16 s, with excellent selectivity.

Enzymatic Low Volume Passive Sweat Based Assays for Multi-Biomarker Detection

Simultaneous detection of correlated multi-biomarkers on a single low-cost platform in ultra-low fluid volumes with robustness is in growing demand for the development of wearable diagnostics. A non-faradaic biosensor for the simultaneous detection of alcohol, glucose, and lactate utilizing low volumes (1–5 μL) of sweat is demonstrated. Biosensing is implemented using nanotextured ZnO films integrated on a flexible porous membrane to achieve enhanced sensor performance. The ZnO sensing region is functionalized with enzymes specific for the detection of alcohol, glucose, and lactate in the ranges encompassing their physiologically relevant levels. A non-faradaic chronoamperometry technique is used to measure the current changes associated with interactions of the target biomarkers with their specific enzyme. The specificity performance of the biosensing platform was established in the presence of cortisol as the non-specific molecule. Biosensing performance of the platform in a continuous mode performed over a 1.5-h duration showed a stable current response to cumulative lifestyle biomarker concentrations with capability to distinguish reliably between low, mid, and high concentration ranges of alcohol (0.1, 25, 100 mg/dL), glucose (0.1, 10, 50 mg/dL), and lactate (1, 50, 100 mM). The low detection limits and a broader dynamic range for the lifestyle biomarker detection are quantified in this research demonstrating its suitability for translation into a wearable device.