Point of care testing system via enzymatic method for the rapid, efficient assay of glycated albumin

Boronate crosslinking-based ratiometric electrochemical assay of glycated albumin

As a product of nonenzymatic glycation, glycated albumin (GA) is a promising serum marker for the short-term glycemic monitoring in patients with diabetes. On the basis of the boronate crosslinking (BCL)-enabled direct labeling of ferrocene (Fc) tags to the nonenzymatically glycated (NEG) sites, we report herein a novel aptamer-based ratiometric electrochemical (apt-REC) platform for the point-of-care (POC) assay of GA. This apt-REC platform is based on the recognition of GA proteins by the methylene blue (MB)-modified aptamer receptors and the labeling of the Fc tags to the NEG sites via the BCL. Using MB as the reference tag and Fc as the quantification tag, the ratio of the oxidation currents (i.e., IFc/IMB) can serve as the yardstick for the ratiometric assay of GA. Due to the presence of tens of the NEG sites, each GA protein can be labeled with tens of quantification tags, permitting the amplified assay in a simple, time-saving, and low-cost manner. The ratiometric signal exhibited a good linear response over the range from 0.1 to 100 μg/mL, with a detection limit of 45.5 ng/mL. In addition to the superior reproducibility and robustness, this apt-REC platform is highly selective (capable of discriminating GA against human serum albumin (HSA)) and applicable to GA assay in serum samples. Due to its low cost, high reproducibility and robustness, simple operation, and high sensitivity and selectivity, this apt-REC platform holds great promise in the POC assay of GA for diabetes management.

Analytical Challenges in Diabetes Management: Towards Glycated Albumin Point-of-Care Detection

Diabetes mellitus is a worldwide-spread chronic metabolic disease that occurs when the pancreas fails to produce enough insulin levels or when the body fails to effectively use the secreted pancreatic insulin, eventually resulting in hyperglycemia. Systematic glycemic control is the only procedure at our disposal to prevent diabetes long-term complications such as cardiovascular disorders, kidney diseases, nephropathy, neuropathy, and retinopathy. Glycated albumin (GA) has recently gained more and more attention as a control biomarker thanks to its shorter lifespan and wider reliability compared to glycated hemoglobin (HbA1c), currently the “gold standard” for diabetes screening and monitoring in clinics. Various techniques such as ion exchange, liquid or affinity-based chromatography and immunoassay can be employed to accurately measure GA levels in serum samples; nevertheless, due to the cost of the lab equipment and complexity of the procedures, these methods are not commonly available at clinical sites and are not suitable to home monitoring. The present review describes the most up-to-date advances in the field of glycemic control biomarkers, exploring in particular the GA with a special focus on the recent experimental analysis techniques, using enzymatic and affinity methods. Finally, analysis steps and fundamental reading technologies are integrated into a processing pipeline, paving the way for future point-of-care testing (POCT). In this view, we highlight how this setup might be employed outside a laboratory environment to reduce the time from measurement to clinical decision, and to provide diabetic patients with a brand-new set of tools for glycemic self-monitoring.

Analyzation of the binding mechanism and the isoelectric point of glycated albumin with self-assembled, aptamer-conjugated films by using surface plasmon resonance

Glycated albumin(GA), a biomarker which has great potential to replace glycated hemoglobin in the diagnosis and treatment of diabetes, is being extensively studied by scientists, especially in preventive medicine. Aptamers, as novel probes, have attracted much attention due to their high specificity, wide storage conditions, and simple preparation. However, the interaction mechanism between GA and its aptamer is still unclear, hindering the progress of diabetic aptamer sensors into clinical testing. In this study, the interaction mechanism between GA and its aptamer was evaluated for the first time using surface plasmon resonance by changing the pH value, salt concentration and temperature. The successful preparation of the sensor chip is proved by the water contact angle, Atomic Force Microscope, and the X-ray photoelectron spectroscopy. This study shows that the pH can greatly affect the formation of a complex from the interaction between the aptamer and GA. The interaction mechanism between GA aptamer and GA was caused by electrostatic force. Otherwise, this is the first time to detect protein isoelectric point (pI) using SPR. This study provides an important reference for researchers of aptamer sensors from the perspective of detection environment, and promotes the use of aptamer sensors to the clinic.

A ratiometric electrochemical biosensor for glycated albumin detection based on enhanced nanozyme catalysis of cuprous oxide-modified reduced graphene oxide nanocomposites

Nanozymes have enzyme-like characteristics and nanozyme-based electrochemical sensors have been widely studied for biomarker detection. In this work, cuprous oxide-modified reduced graphene oxide (Cu₂O-rGO) nanozyme was prepared by simultaneous reduction of copper chloride and graphene oxide. This Cu₂O-rGO nanozyme displayed an outstanding electrocatalytic activity to glucose oxidation and was used as the modified material of a glassy carbon electrode to fabricate an electrochemical ratiometric biosensor for glycated albumin (GA) detection. In this ratiometric biosensor, methylene blue-labeled DNA tripods (MB-tDNA) were adsorbed on the Cu₂O-rGO/GCE surface to form a bioinspired electrode (MB-tDNA/Cu₂O-rGO/GCE), in which the catalytic sites of Cu₂O-rGO were covered by MB-tDNA. In the presence of target GA, GA could be identified by the aptamer sequence contained in MB-tDNA, and a MB-tDNA/GA complex was formed and released into the solution, so the reduced current of MB-tDNA was decreased. Simultaneously, the oxidized current of the outer added glucose was increased since more catalytic sites of Cu₂O-rGO nanozyme on the substrate electrode surface were exposed. The ratio of the peak currents of glucose oxidation and methylene blue reduction (I_Glu/I_MB) was used to monitor the GA level and ultimately improve the accuracy of the method. The electrochemical sensor showed a low detection limit of 0.007 μg mL^-1 and a wide linear range from 0.02 to 1500 μg mL^-1. The proposed sensor was also successfully used to measure the GA expression level in the blood serum of a diabetic mouse model.

Glycation ratio determination through simultaneous detection of human serum albumin and glycated albumin on an advanced lateral flow immunoassay sensor

Glycated albumin synthesized in a non-enzymatic reaction with high glucose levels in human plasma is a long-term biomarker for understanding average glucose levels over the past few weeks. Glycated albumin level determination requires an enzymatic assay involving an expensive, complicated, and laborious process, including the specific hydrolysis of albumin and the oxidation of glycated amino acids. In this study, we developed two advanced lateral flow immunoassays (LFIAs) for the simultaneous determination of total human serum albumin and glycated albumin concentrations using a colorimetric signal. Additionally, through a sequential reaction on our advanced LFIA, the selectivity of glycated albumin was improved. We quantified both HSA and GA with wide detection ranges of 1 ng mL^-1-1 mg mL^-1 and 0.5 μg mL^-1-3.6 mg mL^-1, respectively. Various serum samples with different glycation ratios were analyzed using this sensor and demonstrated a reasonable recovery range. This indicated that our platform could directly determinate the glycation ratio of various samples, and therefore, be applicable in point-of-care glucose status monitoring.

Aptasensor based optical detection of glycated albumin for diabetes mellitus diagnosis

Glycated albumin (GA) has been reported as an important biomarker for diabetes mellitus. This study investigates an optical sensor comprised of deoxyribonucleic acid (DNA) aptamer, semiconductor quantum dot and gold (Au) nanoparticle for the detection of GA. The system functions as a 'turn on' sensor because an increase in photoluminescence intensity is observed upon the addition of GA to the sensor. This is possibly because of the structure of the DNA aptamer, which folds to form a large hairpin loop before the addition of the analyte and is assumed to open up after the addition of target to the sensor in order to bind to GA. This pushes the quantum dot and the Au nanoparticle away causing an increase in photoluminescence. A linear increase in photoluminescence intensity and quenching efficiency of the sensor is observed as the GA concentration is varied between 0-14 500 nM. Time based photoluminescence studies with the sensor show the decrease in binding rate of the aptamer to the target within a specific time period. The sensor was found to have a higher selectivity towards GA than other control proteins. Further investigation of this simple sensor with greater number of clinical samples can open up avenues for an efficient diagnosis and monitoring of diabetes mellitus when used in conjunction with the traditional method of glucose level monitoring.

A microfluidic paper-based analytical device for the assay of albumin-corrected fructosamine values from whole blood samples

BACKGROUND

A method for acquiring albumin-corrected fructosamine values from whole blood using a microfluidic paper-based analytical system that offers substantial improvement over previous methods is proposed.

RESULTS

The time required to quantify both serum albumin and fructosamine is shortened to 10 min with detection limits of 0.50 g dl(-1) and 0.58 mM, respectively (S/N = 3). The proposed system also exhibited good within-run and run-to-run reproducibility. The results of the interference study revealed that the acceptable recoveries ranged from 95.1 to 106.2%. The system was compared with currently used large-scale methods (n = 15), and the results demonstrated good agreement among the techniques.

CONCLUSION

The microfluidic paper-based system has the potential to continuously monitor glycemic levels in low resource settings.

Construction of engineered fructosyl peptidyl oxidase for enzyme sensor applications under normal atmospheric conditions

Current enzymatic methods for the analysis of glycated proteins use flavoenzymes that catalyze the oxidative deglycation of fructosyl peptides, designated as fructosyl peptidyl oxidases (FPOXs). However, as FPOXs are oxidases, the signals derived from electron mediator-type electrochemical monitoring based on them are affected by dissolved O(2). Improvement of dye-mediated dehydrogenase activity of FPOXs and its application to enzyme electrode construction were therefore undertaken. Saturation mutagenesis study on Asn56 of FPOX from Phaeosphaeria nodorum, produced mutants with marked decreases in the catalytic ability to employ O(2) as the electron acceptor, while showing higher dye-mediated dehydrogenase activity employing artificial electron acceptors than the parental enzyme. Thus constructed virtually fructosyl peptide dehydrogenase, Asn56Ala, was then applied to produce an enzyme electrode for the measurement of fructosyl-(α) N-valyl-histidine (f-(α)Val-His), the protease-digested product of HbA1c. The enzyme electrode could measure f-(α)Val-His in the physiological target range in air.

Combined assessment of glycated albumin and fasting plasma glucose improves the detection of diabetes in Chinese subjects

1. The aim of the present study was to assess the validity of glycated albumin (GA) and fasting plasma glucose (FPG) as a screening tool for the early detection of diabetes in Chinese subjects. 2. A total of 1971 outpatient subjects underwent a 75 g oral glucose tolerance test (OGTT) and GA measurement. The receiver operating characteristic curve (ROC) was plotted to examine the sensitivity, specificity, and positive and negative predictive values of GA and FPG in detecting undiagnosed diabetes at the different cut-off levels. 3. The prevalence of impaired glucose regulation and diabetes was 27.40% and 38.30%. For these diabetic individuals, 4.64% had isolated fasting hyperglycemia, 50.86% had isolated postprandial hyperglycemia and 44.50% had both. Using ROC analysis, a GA of 17.1% gave an optimal sensitivity of 76.82% (95% confidence interval: 73.64-79.79%) and specificity of 76.89% (74.42-79.23%) for the diagnosis of diabetes. Likewise, a FPG of 6.1 mmol/L gave an optimal sensitivity of 80.93% (77.94-83.67%) and specificity of 85.94% (83.86-87.84%). If subjects met both criteria, they were regarded as having diabetes; the positive predictive value of the combined criteria, FPG ≥ 6.1 mmol/L and GA ≥ 17.1%, was relatively high (84.79% (81.62-87.60%)), and this would have avoided 76% of the OGTT in our survey. 4. In conclusion, a GA value of 17.1%, an optimal cut-off in Chinese subjects, identified a high proportion of potential diabetic individuals. Simultaneous measurement of FPG and GA would enhance the sensitivity of diabetes screening in our population and avoid 76% of OGTT.

Synthesis of tethered poly(N-isopropylacrylamide) for detection of breast cancer recurrence DNA

We have grafted temperature-responsive tethered poly(N-isopropylacrylamide) (PNIPAAm) onto silicon surfaces through atom transfer radical polymerization (ATRP) as a medium to extract human genomic DNA molecules from a biological specimen, namely human blood incorporating target DNA (hgDNA584) and control DNA (hgDNA528) at concentrations of 0.5, 1, and 50 ng μL(-1). The variable adhesion forces of the tethered PNIPAAm brushes on the surfaces were used to capture and release DNA molecules through changes in temperature. After amplifying the signal of the hgDNA584 and hgDNA528 strands released from the tethered PNIPAAm on the substrate using the polymerase chain reaction (PCR), we identified these DNA macromolecules using agarose gel electrophoresis. The accuracy of the detection of hgDNA584 and hgDNA528 was controlled through the design of specific primers in the PCR process. The quantities of these two DNA molecules obtained through the capture and release from tethered PNIPAAm brushes under temperature tuning conditions were sufficient for them to be amplified recognizably, suggesting that this approach could be used in miniaturized lab-on-a-chip cartridges for rapid disease diagnosis.

A review of glycated albumin as an intermediate glycation index for controlling diabetes

INTRODUCTION

This article reviews glycated albumin (GA) as a potential intermediate-term glycation index to fill the gap between self-monitoring of blood glucose (SMBG) and hemoglobin A1c testing in diabetes management. The introduction gives an assessment of available short-, medium-, and long-term glycemic indicators. METHODOLOGIES AND UTILITY: Methods of GA measurement are summarized, and the variance of normal and diabetic GA values are discussed. Greatest uniformity in GA measurement is generally associated with immunoassay and the newer affinity chromatography methodologies utilized by reference laboratories. Utility of GA measurement includes its value as a marker for glycation, its substantial relationship to diabetes complications such as nephropathy and coronary artery disease, and as an unambiguous indicator of glycemic control in diabetes patients undergoing hemodialysis. Studies support the utility of GA in detecting short-term changes in glycemic control, and GA testing has been strongly recommended for gestational diabetes.

RESULTS AND DISCUSSION

The results of a survey with mailings to over 3500 diabetes care professionals primarily in the United States are outlined and analyzed (margin of error: +/-6.5%, 95% confidence). Respondents strongly supported the need for a test for intermediate glycemic control as well as the utility of a rapid GA test as a monthly glycemic indicator.

CONCLUSIONS

Such a test, as yet unavailable, could increase compliance and enhance empowerment among diabetes patients. It also has the potential to reduce the number of recommended SMBG tests, which may result in significant health care cost savings.