Gold Nanostar Colorimetric Detection of Fructosyl Valine as a Potential Future Point of Care Biosensor Candidate for Glycated Haemoglobin Detection

Sensitive electrochemical detection of glycated hemoglobin (HbA1c) using cobalt metal-organic framework/two-dimensional molybdenum diselenide nanocomposite-based immunosensors amplified by polyoxometalate/DNA aptamer

Clinical diagnosis and long-term diabetes management are advanced by monitoring glycated hemoglobin A1c (HbA1c) levels. New sensitive sandwich-like immunosensors for the diagnosis of early diabetes toward detecting HbA1c and hemoglobin (Hb) are demonstrated for the first time. DNA aptamers are used for signal amplification in the sensors for the detection of HbA1c and Hb. The immunosensors are constructed by coating with a cobalt-based metal-organic framework (Co-MOF)/two-dimensional molybdenum diselenide (2D MoSe2) composite onto a working electrode of an ItalSens screen-printed electrode (SPE) inserted into a Sensit/Smart Potentiostat affixed to a smartphone. After the immobilization of the antibodies, the detection is obtained by incubating the resultant SPEs in target solutions and then detecting the response of Keggin-type polyoxometalate (POM) bound on the DNA aptamer chains. In the selected potential window, the POM (silicotungstic acid, H4[α-SiW12O40]) used in this study exhibits the electron-transfer processes I and II ([α-SiW12O40]4-/5- and [α-SiW12O40]5-/6-, respectively) in the acidic buffer electrolyte. Our proposed device demonstrates exceptional performance in the recovery test of %HbA1c in healthy human plasma samples. The sensitivity, selectivity, and stability of this immunosensor are exceedingly outstanding, which makes it one of the potential analytical devices for diagnosing early diabetes by a %HbA1c assay.

WaveFlex biosensor based on S-tapered and waist-expanded technique for detection of glycosylated hemoglobin

Glycosylated hemoglobin (HbA1c) is considered a new standard for the detection of diabetes mellitus because it is more accurate than regular blood sugar tests and there is no need to take blood on an empty stomach or at a specific time. In this work, we have developed a novel optical fiber biosensor, referred to as the "WaveFlex biosensor," which operates on the principles of localized surface plasmon resonance (LSPR) plasmonic wave. The sensor is fabricated using an innovative S-tapered and waist-expanded technique, enabling it to effectively detect HbA1c. Compared to the HbA1c sensors currently in use, HbA1c optical fiber sensors possess the characteristics of high sensitivity, low cost, and strong anti-interference ability. The gold nanoparticles (AuNPs), cerium oxide (CeO2) nanorods (NRs), and tungsten disulfide (WS2) nanosheets (NSs) are functionalized to improve the effectiveness of the fiber sensor on the probe surface. AuNPs are utilized to generate LSPR by the excitation of evanescent waves to amplify the sensing signal. The CeO2-NRs can have a strong metal-carrier interaction with AuNPs, enhancing the cascade of CeO2-NRs and AuNPs. The WS2-NSs with layered fold structure have a large specific surface area. Therefore, the combination of CeO2-NRs and WS2-NSs is conducive to the binding of antibodies and the addition of sites. The functionalized antibodies on the fiber make the sensor probe capable of specific selection. The developed probe is applied to test the HbA1c solution over concentrations of 0-1000 µg/mL, and the sensitivity and limits of detection of 1.195×10-5 a.u./(µg/mL) and 1.66 µg/mL are obtained, respectively. The sensor probe is also evaluated using assays for reproducibility, reusability, selectivity, and pH. According to the findings, a novel method for detecting blood glucose based on a plasmonic biosensor is proposed.

Mechanobactericidal, Gold Nanostar Hydrogel-Based Bandage for Bacteria-Infected Skin Wound Healing

The emergence of multidrug resistant (MDR) microorganisms has led to the development of alternative approaches for providing relief from microbial attacks. The mechano-bactericidal action as a substitute for antimicrobials has become the focus of intensive research. In this work, nanostructure-conjugated hydrogel are explored as a flexible dressing against Staphylococcus aureus (S. aureus)-infected skin wounds. Herein gold nanostars (AuNst) with spike lengths reaching 120 nm are probed for antibacterial action. The bacterial killing of >95% is observed for Pseudomonas aeruginosa (P. aeruginosa) and Escherichia coli (E. coli), while up to 60% for Gram-positive S. aureus. AuNst conjugated hydrogel (AuNst₁₂₀@H) reduced >80% colonies of P. aeruginosa and E. coli. In comparison, around 35.4% reduction of colonies are obtained for S. aureus. The viability assay confirmed the presence of about 85% of living NIH-3T3 cells when grown with hydrogels. An animal wound model is also developed to assess the efficiency of AuNst₁₂₀@H. A significant reduction in wound size is observed on the 10th day in AuNst₁₂₀@H treated animals with fully formed epidermal layers, hair follicles, new blood vessels, and arrector muscles. These findings suggest that novel dressing materials can be developed with antimicrobial nanotextured surfaces.

Glycated Hemoglobin and Methods for Its Point of Care Testing

Glycated hemoglobin (HbA1c) is a product of the spontaneous reaction between hemoglobin and elevated glucose levels in the blood. It is included among the so-called advanced glycation end products, of which is the most important for the clinical diagnosis of diabetes mellitus, and it can serve as an alternative to glycemia measurement. Compared to the diagnosis of diabetes mellitus by glycemia, the HbA1c level is less influenced by a short-term problem with diabetes compensation. Mass spectroscopy and chromatographic techniques are among the standard methods of HbA1c level measurement. Compared to glycemia measurement, there is lack of simple methods for diabetes mellitus diagnosis by means of the HbA1c assay using a point-of-care test. This review article is focused on the surveying of facts about HbA1c and its importance in diabetes mellitus diagnosis, and surveying standard methods and new methods suitable for the HbA1c assay under point-of-care conditions. Various bioassays and biosensors are mentioned and their specifications are discussed.

Enhancement of the Peroxidase-Like Activity of Iodine-Capped Gold Nanoparticles for the Colorimetric Detection of Biothiols

A colorimetric assay was developed for the detection of biothiols, based on the peroxidase-like activity of iodine-capped gold nanoparticles (AuNPs). These AuNPs show a synergetic effect in the form of peroxidase-mimicking activity at the interface of AuNPs, while free AuNPs and iodine alone have weak catalytic properties. Thus, iodine-capped AuNPs possess good intrinsic enzymatic activity and trigger the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), leading to a change in color from colorless to yellow. When added to solution, biothiols, such as cysteine, strongly bind to the interface of AuNPs via gold-thiol bonds, inhibiting the catalytic activity of AuNPs, resulting in a decrease in oxidized TMB. Using this strategy, cysteine could be linearly determined, at a wide range of concentrations (0.5 to 20 μM), with a detection limit of 0.5 μM using UV-Vis spectroscopy. This method was applied for the detection of cysteine in diluted human urine.

Analytical techniques for the detection of glycated haemoglobin underlining the sensors

The increase in concentrations of blood glucose results arise in the proportion of glycated haemoglobin. Therefore, the percentage of glycated haemoglobin in the blood could function as a biomarker for the average glucose level over the past three months and can be used to detect diabetes. The study of glycated haemoglobin tends to be complex as there are about three hundred distinct assay techniques available for evaluating glycated haemoglobin which contributes to some differences in the recorded values from the similar samples. This review outlines distinct analytical methods that have evolved in the recent past for precise recognition of the glycated - proteins.

Gold nanostars-diagnosis, bioimaging and biomedical applications

Gold Nanostars (GNS) have attracted tremendous attention toward themselves owing to their multi-branched structure and unique properties. These state of the art metallic nanoparticles possess intrinsic features like remarkable optical properties and exceptional physiochemical activities. These star-shaped gold nanoparticles can predominantly be utilized in biosensing, photothermal therapy, imaging, surface-enhanced Raman spectroscopy and target drug delivery applications due to their low toxicity and extraordinary optical features. In the current review, recent approaches in the matter of GNS in case of diagnosis, bioimaging and biomedical applications were summarized and reported. In this regard, first an overview about the structure and general properties of GNS were reported and thence detailed information regarding the diagnostic, bioimaging, photothermal therapy, and drug delivery applications of such novel nanomaterials were presented in detail. Summarized information clearly highlighting the superior capability of GNS as potential multi-functional materials for biomedical applications.