Sensitivity Detection of Uric Acid and Creatinine in Human Urine Based on Nanoporous Gold

Reliable quantitative detection of uric acid in urine by surface-enhanced Raman spectroscopy with endogenous internal standard

Abnormal levels of uric acid (UA) in urine serve as warning signs for gout and metabolic cardiovascular diseases, necessitating the monitoring of UA levels for early prevention. However, the current analytical methods employed suffer from limitations in terms of inadequate suitability for home-based applications and the requirement of non-invasive procedures. In this approach, creatinine, a metabolite with a constant excretion rate, was incorporated as an endogenous internal standard (e-IS) for calibration, presenting a rapid, pretreatment-free, and accurate strategy for quantitative determination of UA concentrations. By utilizing urine creatinine as an internal reference value to calibrate the signal fluctuation of surface-enhanced Raman spectroscopy (SERS) of UA, the quantitative accuracy can be significantly improved without the need for an external internal standard. Due to the influence of the medium, UA, which carries a negative charge, is selectively adsorbed by Au@Ag nanoparticles functionalized with hexadecyltrimethylammonium chloride (CTAC) in this system. Furthermore, a highly convenient detection method was developed, which eliminates the need for pre-processing and minimizes matrix interference by simple dilution. The method was applied to the urine detection of different volunteers, and the results were highly consistent with those obtained using the UA colorimetric kit (UACK). The detection time of SERS was only 30 s, which is 50 times faster than UACK. This quantitative strategy of using urinary creatinine as an internal standard to correct the SERS intensity of uric acid is also expected to be extended to the quantitative detection needs of other biomarkers in urine.

Rapid Detection of the Anti-Tumor Drug Etoposide in Biological Samples by Using a Nanoporous-Gold-Based Electrochemical Sensor

Monitoring etoposide is important due to its wide usage in anti-tumor therapy; however, the commonly used HPLC method is expensive and often requires complicated extraction and detection procedures. Electrochemical analysis has great application prospects because of its rapid response and high specificity, sensitivity, and efficiency with low cost and high convenience. In this study, we constructed a nanoporous gold (NPG)-modified GCE for the detection of etoposide. The electrochemical oxidation of etoposide by NPG caused a sensitive current peak at +0.27 V with good reproductivity in 50 mM of phosphate buffer (pH 7.4). The relationship between etoposide concentration and peak current was linear in the range between 0.1 and 20 μM and between 20 and 150 μM, with a detection sensitivity of 681.8 μA mM-1 cm-2 and 197.2 μA mM-1 cm-2, respectively, and a limit of detection (LOD) reaching 20 nM. The electrode had a good anti-interference ability to several common anions and cations. Spiked recovery tests in serum, urine, and fermentation broth verified the excellent performance of the sensor in terms of sensitivity, reproducibility, and specificity. This may provide a promising tool for the detection of etoposide in biological samples.

Simultaneous recognition of dopamine and uric acid in real samples through highly sensitive new electrode fabricated using ZnO/carbon quantum dots: bio-imaging and theoretical studies

Dopamine (DA) and uric acid (UA), which are vital components in human metabolism, cause several health problems if they are present in altered concentrations; thus, the determination of DA and UA is essential in real samples using selective sensors. In the present study, graphite carbon paste electrodes (CPE) were fabricated using ZnO/carbon quantum dots (ZnO/CQDs) and employed as electrochemical sensors for the detection of DA and UA. These electrodes were fully characterized via different analytical techniques (XRD, SEM, TEM, XPS, and EDS). The electrochemical responses from the modified electrodes were evaluated using cyclic voltammetry, square wave voltammetry, and electrochemical impedance spectroscopy. The results showed that the present electrode has exhibited high sensitivity towards DA, recognizing even at low concentrations (0.12 μM), and no inference was observed in the presence of UA. The ZnO/CQD electrode was applied for the simultaneous detection of co-existing DA and UA in real human urine samples and the peak potential separation between DA and UA was found to be greatly associated with the synergistic effect originated from ZnO and CQDs. The limit of detection (LOD) of the electrode was analyzed, and compared with other commercially available electrodes. Thus, the ZnO/CQD electrode was used to detect DA and UA in real samples, such as Saccharomyces cerevisiae cells.

Integration of Glutamate Dehydrogenase and Nanoporous Gold for Electrochemical Detection of Glutamate

Glutamate, a non-essential amino acid produced by fermentation, plays a significant role in disease diagnosis and food safety. It is important to enable the real-time monitoring of glutamate concentration for human health and nutrition. Due to the challenges in directly performing electrochemical oxidation-reduction reactions of glutamate, this study leverages the synergistic effect of glutamate dehydrogenase (GLDH) and nanoporous gold (NPG) to achieve the indirect and accurate detection of glutamate within the range of 50 to 700 μM by measuring the generated quantity of NADH during the enzymatic reaction. The proposed biosensor demonstrates remarkable performance characteristics, including a detection sensitivity of 1.95 μA mM-1 and a limit of detection (LOD) of 6.82 μM. The anti-interference tests indicate an average recognition error ranging from -3.85% to +2.60%, spiked sample recovery rates between 95% and 105%, and a relative standard deviation (RSD) of less than 4.97% for three replicate experiments. Therefore, the GLDH-NPG/GCE biosensor presented in this work exhibits excellent accuracy and repeatability, providing a novel alternative for rapid glutamate detection. This research contributes significantly to enhancing the precise monitoring of glutamate concentration, thereby offering more effective guidance and control for human health and nutrition.

Electrochemical Nanosensors for Sensitization of Sweat Metabolites: From Concept Mapping to Personalized Health Monitoring

Sweat contains a broad range of important biomarkers, which may be beneficial for acquiring non-invasive biochemical information on human health status. Therefore, highly selective and sensitive electrochemical nanosensors for the non-invasive detection of sweat metabolites have turned into a flourishing contender in the frontier of disease diagnosis. A large surface area, excellent electrocatalytic behavior and conductive properties make nanomaterials promising sensor materials for target-specific detection. Carbon-based nanomaterials (e.g., CNT, carbon quantum dots, and graphene), noble metals (e.g., Au and Pt), and metal oxide nanomaterials (e.g., ZnO, MnO2, and NiO) are widely used for modifying the working electrodes of electrochemical sensors, which may then be further functionalized with requisite enzymes for targeted detection. In the present review, recent developments (2018-2022) of electrochemical nanosensors by both enzymatic as well as non-enzymatic sensors for the effectual detection of sweat metabolites (e.g., glucose, ascorbic acid, lactate, urea/uric acid, ethanol and drug metabolites) have been comprehensively reviewed. Along with this, electrochemical sensing principles, including potentiometry, amperometry, CV, DPV, SWV and EIS have been briefly presented in the present review for a conceptual understanding of the sensing mechanisms. The detection thresholds (in the range of mM-nM), sensitivities, linear dynamic ranges and sensing modalities have also been properly addressed for a systematic understanding of the judicious design of more effective sensors. One step ahead, in the present review, current trends of flexible wearable electrochemical sensors in the form of eyeglasses, tattoos, gloves, patches, headbands, wrist bands, etc., have also been briefly summarized, which are beneficial for on-body in situ measurement of the targeted sweat metabolites. On-body monitoring of sweat metabolites via wireless data transmission has also been addressed. Finally, the gaps in the ongoing research endeavors, unmet challenges, outlooks and future prospects have also been discussed for the development of advanced non-invasive self-health-care-monitoring devices in the near future.