Simple and label-free strategy for terminal transferase assay using a personal glucose meter

Recent Developments in Personal Glucose Meters as Point-of-Care Testing Devices (2020-2024)

Point-of-care testing (POCT) is a contemporary diagnostic approach characterized by its user-friendly nature, cost efficiency, environmental compatibility, and lack of reliance on professional experts. Therefore, it is widely used in clinical diagnosis and other analytical testing fields to meet the demand for rapid and convenient testing. The application of POCT technology not only improves testing efficiency, but also brings convenience and benefits to the healthcare industry. The personal glucose meter (PGM) is a highly successful commercial POCT tool that has been widely used not only for glucose analysis, but also for non-glucose target detection. In this review, the recent advances from 2020 to 2024 in non-glucose target analysis for PGMs as POCT devices are summarized. The signal transduction strategies for non-glucose target analysis based on PGMs, including enzymatic transduction, nanocarrier transduction (enzyme or glucose), and glucose consumption transduction are briefly introduced. Meanwhile, the applications of PGMs in non-glucose target analysis are outlined, encompassing biomedical, environmental, and food analysis, along with other diverse applications. Finally, the prospects of and obstacles to employing PGMs as POCT tools for non-glucose target analysis are discussed.

Detection of terminal deoxynucleotidyl transferase activity based on self-mediated nucleic acid elongation and elemental labeling inductively coupled plasma-mass spectrometry

Terminal deoxynucleotidyl transferase (TdT), a specialized DNA polymerase, is recognized as a promising biomarker for acute leukemia. Herein, taking the advantage of the self-mediated strand elongation property of TdT, a simple and sensitive method for TdT activity assay was developed based on gold nanoparticles (AuNPs) labeling inductively coupled plasma mass spectrometry (ICP-MS). In the presence of TdT, the primer DNA on magnetic beads is elongated with an adenine-rich single stranded long chain that can label poly-thymine modified AuNPs. After acid elution, the labeled AuNPs were detected by ICP-MS, and the signal intensity of 197Au reflected the TdT activity. Under the optimal conditions, the limit of detection for TdT activity is down to 0.054 U mL-1, along with good selectivity and strong tolerance to other interfering proteins. Furthermore, it achieves a straightforward and accurate detection of TdT activity in acute lymphoblastic leukemia cells without sample pre-processing and tool enzyme addition. Therefore, the proposed method shows great promise as a valuable tool for TdT-related biological research and leukemia therapeutics.

A personal glucose meter-utilized strategy for portable and label-free detection of hydrogen peroxide

Rapid and precise detection of hydrogen peroxide (H2O2) holds great significance since it is linked to numerous physiological and inorganic catalytic processes. We herein developed a label-free and washing-free strategy to detect H2O2 by employing a hand-held personal glucose meter (PGM) as a signal readout device. By focusing on the fact that the reduced redox mediator ([Fe(CN)6]4-) itself is responsible for the final PGM signal, we developed a new PGM-based strategy to detect H2O2 by utilizing the target H2O2-mediated oxidation of [Fe(CN)6]4- to [Fe(CN)6]3- in the presence of horseradish peroxidase (HRP) and monitoring the reduced PGM signal in response to the target amount. Based on this straightforward and facile design principle, H2O2 was successfully determined down to 3.63 μM with high specificity against various non-target molecules. We further demonstrated that this strategy could be expanded to identify another model target choline by detecting H2O2 produced through its oxidation promoted by choline oxidase. Moreover, we verified its practical applicability by reliably determining extracellular H2O2 released from the breast cancer cell line, MDA-MB-231. This work could evolve into versatile PGM-based platform technology to identify various non-glucose target molecules by employing their corresponding oxidase enzymes, greatly advancing the portable biosensing technologies.

Target-initiated fluorescent aptasensor based on multisite strand displacement amplification for label-free detection of ochratoxin A

We developed a fluorescent aptasensor for label-free detection of ochratoxin A (OTA) based on TdT- and DNA polymerase-assisted multisite strand displacement amplification. This aptasensor exhibits good specificity and high sensitivity with a limit of detection (LOD) of 0.18 ng mL-1, and it can be further applied for the accurate quantification of OTA in complex real samples, holding promising applications in the field of food safety.

Nanomaterials with Glucose Oxidase-Mimicking Activity for Biomedical Applications

Glucose oxidase (GOD) is an oxidoreductase that catalyzes the aerobic oxidation of glucose into hydrogen peroxide (H₂O₂) and gluconic acid, which has been widely used in industrial raw materials production, biosensors and cancer treatment. However, natural GOD bears intrinsic disadvantages, such as poor stability and a complex purification process, which undoubtedly restricts its biomedical applications. Fortunately, several artificial nanomaterials have been recently discovered with a GOD-like activity and their catalytic efficiency toward glucose oxidation can be finely optimized for diverse biomedical applications in biosensing and disease treatments. In view of the notable progress of GOD-mimicking nanozymes, this review systematically summarizes the representative GOD-mimicking nanomaterials for the first time and depicts their proposed catalytic mechanisms. We then introduce the efficient modulation strategy to improve the catalytic activity of existing GOD-mimicking nanomaterials. Finally, the potential biomedical applications in glucose detection, DNA bioanalysis and cancer treatment are highlighted. We believe that the development of nanomaterials with a GOD-like activity will expand the application range of GOD-based systems and lead to new opportunities of GOD-mimicking nanomaterials for various biomedical applications.

CRISPR/Cas13a-assisted AMP generation for SARS-CoV-2 RNA detection using a personal glucose meter

Herein, we described a washing- and label-free clustered regularly interspaced short palindromic repeats (CRISPR)/LwaCas13a-based RNA detection method utilizing a personal glucose meter (PGM), which relies on the trans-cleavage activity of CRISPR/Cas13a and kinase reactions. In principle, the presence of target RNA activates the trans-cleavage of CRISPR/Cas13a, generating 2',3'-cyclic phosphate adenosine, which is converted to adenosine monophosphate (AMP) by the T4 polynucleotide kinase. Subsequently, the AMP is converted to adenosine diphosphate (ADP) through phosphorylation by a myokinase; ADP is then used as a substrate in the cascade enzymatic reaction promoted by pyruvate kinase and hexokinase. The overall reaction leads to the continuous conversion of glucose to glucose-6-phosphate, resulting in a reduction of glucose concentration proportional to the level of target RNA, which can therefore be indirectly measured with a PGM. By employing this novel strategy, severe acute respiratory syndrome coronavirus-2 RNA can be successfully detected with excellent specificity. In addition, we were able to overcome non-specific responses of CRISPR/Cas13a and distinguish single nucleotide polymorphisms by introducing a single-base mismatch in the complementary RNA. Our study provides an alternative coronavirus disease 2019 detection technology that is affordable, accessible, and portable with a fast turnaround time and excellent selectivity.

Washing-Free and Label-Free Onsite Assay for Inorganic Pyrophosphatase Activity Using a Personal Glucose Meter

In this study, we demonstrated a personal glucose meter-based method for washing-free and label-free inorganic pyrophosphatase (PPase) detection, which relies on the cascade enzymatic reaction (CER) promoted by hexokinase and pyruvate kinase. In principle, the absence of target PPase enables adenosine triphosphate sulfurylase to catalyze the conversion of pyrophosphate (PPi) to ATP, a substrate of CER, which results in the significant reduction of glucose levels by the effective CER process. In contrast, the PPi cleavage activity works in the presence of target PPase by decomposing PPi to orthophosphate (Pi). Therefore, the CER process cannot be effectively executed, leading to the maintenance of the initial high glucose level that may be measured by a portable personal glucose meter. Based on this novel strategy, a quantitative evaluation of the PPase activity may be achieved in a dynamic linear range of 1.5-25 mU/mL with a detection limit of 1.18 mU/mL. Compared with the previous PPase detection methods, this method eliminates the demand for expensive and bulky analysis equipment as well as a complex washing step. More importantly, the diagnostic capability of this method was also successfully verified by reliably detecting PPase present in an undiluted human serum sample with an excellent recovery ratio of 100 ± 2%.

Research Progress and Prospects of Nanozyme-Based Glucose Biofuel Cells

The appearance and evolution of biofuel cells can be categorized into three groups: microbial biofuel cells (MBFCs), enzymatic biofuel cells (EBFCs), and enzyme-like nanomaterial (nanozyme)-based biofuel cells (NBFCs). MBFCs can produce electricity from waste; however, they have significantly low power output as well as difficulty in controlling electron transfer and microbial growth. EBFCs are more productive in generating electricity with the assistance of natural enzymes, but their vulnerability under diverse environmental conditions has critically hindered practical applications. In contrast, because of the intrinsic advantages of nanozymes, such as high stability and robustness even in harsh conditions, low synthesis cost through facile scale-up, and tunable catalytic activity, NBFCs have attracted attention, particularly for developing wearable and implantable devices to generate electricity from glucose in the physiological fluids of plants, animals, and humans. In this review, recent studies on NBFCs, including the synthetic strategies and catalytic activities of metal and metal oxide-based nanozymes, the mechanism of electricity generation from glucose, and representative studies are reviewed and discussed. Current challenges and prospects for the utilization of nanozymes in glucose biofuel cells are also discussed.

Multimodal/Multifunctional Nanomaterials in (Bio)electrochemistry: Now and in the Coming Decade

Multifunctional nanomaterials, defined as those able to achieve a combined effect or more than one function through their multiple functionalization or combination with other materials, are gaining increasing attention in the last years in many relevant fields, including cargo targeted delivery, tissue engineering, in vitro and/or in vivo diseases imaging and therapy, as well as in the development of electrochemical (bio)sensors and (bio)sensing strategies with improved performance. This review article aims to provide an updated overview of the important advances and future opportunities exhibited by electrochemical biosensing in connection to multifunctional nanomaterials. Accordingly, representative aspects of recent approaches involving metal, carbon, and silica-based multifunctional nanomaterials are selected and critically discussed, as they are the most widely used multifunctional nanomaterials imparting unique capabilities in (bio)electroanalysis. A brief overview of the main remaining challenges and future perspectives in the field is also provided.