Direct electrodeposition of gold nanotube arrays of rough and porous wall by cyclic voltammetry and its applications of simultaneous determination of ascorbic acid and uric acid

Tailor-Made Gold Nanomaterials for Applications in Soft Bioelectronics and Optoelectronics

In modern nanoscience and nanotechnology, gold nanomaterials are indispensable building blocks that have demonstrated a plethora of applications in catalysis, biology, bioelectronics, and optoelectronics. Gold nanomaterials possess many appealing material properties, such as facile control over their size/shape and surface functionality, intrinsic chemical inertness yet with high biocompatibility, adjustable localized surface plasmon resonances, tunable conductivity, wide electrochemical window, etc. Such material attributes have been recently utilized for designing and fabricating soft bioelectronics and optoelectronics. This motivates to give a comprehensive overview of this burgeoning field. The discussion of representative tailor-made gold nanomaterials, including gold nanocrystals, ultrathin gold nanowires, vertically aligned gold nanowires, hard template-assisted gold nanowires/gold nanotubes, bimetallic/trimetallic gold nanowires, gold nanomeshes, and gold nanosheets, is begun. This is followed by the description of various fabrication methodologies for state-of-the-art applications such as strain sensors, pressure sensors, electrochemical sensors, electrophysiological devices, energy-storage devices, energy-harvesting devices, optoelectronics, and others. Finally, the remaining challenges and opportunities are discussed.

Microelectronic fibers for multiplexed sweat sensing

Wearable bioelectronics are gaining extraordinary attention due to their capabilities to achieve continuous monitoring of human health status. However, mainstream manufacturing technologies, including photolithography and printing technology, limit current wearable bioelectronics on 2D planar structures with little surface area in contact with the body. It thus limits the amount of physiological information that current wearable bioelectronics could obtain. Furthermore, they need to be firmly attached to the body, affecting the wearing comfort. In this study, we leveraged the versatile thermal drawing process and developed a flexible microelectronic fiber with bioanalytical functions that could be woven into textiles as a new form of wearable bioelectronics. Within a single strand of fiber, we successfully integrated all-in-one multiplexed electrochemical sensing capabilities, with the sweat as the primary object. Adopting the laser micromachining technique, we developed biosensing functions on the longitudinal surface of the fiber with two sensing electrodes for Na⁺ and uric acid (UA), respectively, together with a pseudo reference electrode (p-RE). We carefully characterized the all-in-one multiplexed sensing performance of the fiber and demonstrated its successful application in sweat sensing based on its textile forms. The results show significant potential for application in wearable textiles for monitoring key health signals of humans.

Theoretical simulation of nonlinear regulation of wall thickness dependent longitudinal surface plasmon in pentagonal gold nanotubes

In this paper, the longitudinal plasmon mode optical properties and localized electric field distribution of a single pentagonal gold nanotube are investigated for the first time by the discrete dipole approximation. It is found that pentagonal gold nanotube has stronger electric field distribution compared with circular gold nanotubes when the incident wavelength is located at the plasmon resonance peak. Additionally, we observed that the longitudinal plasmon resonance peak can blue shift nonlinearly with increasing wall thickness, but red shifts linearly with the increase of the length of the pentagonal gold nanotube. The localized electric field analysis reveals that the longitudinal plasmon peak of the pentagonal gold nanotube originates from the dipole resonance mode. The local electric field intensity is controlled by the wall thickness and length. Notably, the effect of wall thickness on the longitudinal plasmon resonance and electric field enhancement can be attributed to the change of the plasmon coupling position and intensity. This work has enriched the theoretical research of pentagonal gold nanotubes and provided ideas for the preparation of high sensitivity nanoprobes biosensors.

Determination of Ascorbic Acid in Pharmaceuticals and Food Supplements with the New Potassium Ferrocyanide-Doped Polypyrrole-Modified Platinum Electrode Sensor

This paper reports the results obtained from the determination of ascorbic acid with platinum-based voltammetric sensors modified with potassium hexacyanoferrate-doped polypyrrole. The preparation of the modified electrodes was carried out by electrochemical polymerization of pyrrole from aqueous solutions, using chronoamperometry. Polypyrrole films were deposited on the surface of the platinum electrode, by applying a constant potential of 0.8 V for 30 s. The thickness of the polymer film was calculated from the chronoamperometric data, and the value was 0.163 μm. Cyclic voltammetry was the method used for the Pt/PPy-FeCN electrode electrochemical characterization in several types of solution, including KCl, potassium ferrocyanide, and ascorbic acid. The thin doped polymer layer showed excellent sensitivity for ascorbic acid detection. From the voltammetric studies carried out in solutions of different concentrations of ascorbic acid, ranging from 1 to 100 × 10−6 M, a detection limit of 2.5 × 10−7 M was obtained. Validation of the analyses was performed using pharmaceutical products with different concentrations of ascorbic acid, from different manufacturers and presented in various pharmaceutical forms, i.e., intravascular administration ampoules, chewable tablets, and powder for oral suspension.

Quantitative determination of uric acid using paper-based biosensor modified with graphene oxide and 5-amino-1,3,4-thiadiazole-2-thiol

Uric acid is the primary end product of human purine metabolism and has been regarded as a key parameter in urine and blood for monitoring physiological conditions. This paper presents a paper-based biosensor for a quantitative determination of uric acid using electrochemical detection. The working electrode of the biosensor is modified with graphene oxide (GO) and 5-amino-1,3,4-thiadiazole-2-thiol (ATT) by electropolymerizing ATT on the surface of graphene oxide. In this study, cyclic voltammetry (CV) measurements required only 200 μL of analyte solution. The experimental results showed that the oxidation peak current increased as the concentration of uric acid become higher and exhibited a linear relationship in the concentration range of 0.1-10 mM, indicating that this proposed biosensor has high sensitivity. In addition, this biosensor has good selectivity to detect uric acid because ATT has a specific binding with it. In human blood and body fluids, nitrites may be the only factor that can interfere with the detection of uric acid using this proposed biosensor. Nevertheless, uric acid can be discriminated from nitrite in the CV measurement due to different oxidation potentials. Thus, this proposed paper-based biosensor is a promising tool for detecting uric acid in biological samples.

Gold nanotubes: synthesis, properties and biomedical applications

This review (with 106 references) summarizes the latest progress in the synthesis, properties and biomedical applications of gold nanotubes (AuNTs). Following an introduction into the field, a first large section covers two popular AuNTs synthesis methods. The hard template method introduces anodic alumina oxide template (AAO) and track-etched membranes (TeMs), while the sacrificial template method based on galvanic replacement introduces bimetallic, trimetallic AuNTs and AuNT-semiconductor hybrid materials. Then, the factors affecting the morphology of AuNTs are discussed. The next section covers their unique surface plasmon resonance (SPR), surface-enhanced Raman scattering (SERS) and their catalytic properties. This is followed by overviews on the applications of AuNTs in biosensors, protein transportation, photothermal therapy and imaging. Several tables are presented that give an overview on the wealth of synthetic methods, morphology factors and biological application. A concluding section summarizes the current status, addresses current challenges and gives an outlook on potential applications of AuNTs in biochemical detection and drug delivery.Graphical abstract.

Double injection/single detection asymmetric flow injection manifold for spectrophotometric determination of ascorbic acid and uric acid: Selection the optimal conditions by MCDM approach based on different criteria weighting methods

A simple and sensitive double injection/single detector flow injection analysis (FIA) method is proposed for the simultaneous kinetic determination of ascorbic acid (AA) and uric acid (UA). This method is based upon the difference between the rates of the AA and UA reactions with Fe³⁺ in the presence of 1, 10-phenanthroline (phen). The absorbance of Fe²⁺/1, 10-phenanthroline (Fe-phen) complex obtained as the product was measured spectrophotometrically at 510nm. To reach a good accuracy in the differential kinetic determination via the mathematical manipulations of the transient signals, different criteria were considered in the selection of the optimum conditions. The multi criteria decision making (MCDM) approach was applied for the selection of the optimum conditions. The importance weights of the evaluation criteria were determined using the analytic hierarchy process, entropy method, and compromised weighting (CW). The experimental conditions (alternatives) were ranked by the technique for order preference by similarity to an ideal solution. Under the selected optimum conditions, the obtained analytical signals were linear in the ranges of 0.50-5.00 and 0.50-4.00mgL^-1 for AA and UA, respectively. The 3σ detection limits were 0.07mgL^-1 for AA and 0.12mgL^-1 for UA. The relative standard deviations for four replicate determinations of AA and UA were 2.03% and 3.30% respectively. The method was also applied for the analysis of analytes in the blood serum, Vitamine C tablets, and tap water with satisfactory results.

Optimization of modified carbon paste electrode with multiwalled carbon nanotube/ionic liquid/cauliflower-like gold nanostructures for simultaneous determination of ascorbic acid, dopamine and uric acid

We describe the modification of a carbon paste electrode (CPE) with multiwalled carbon nanotubes (MWCNTs) and an ionic liquid (IL). Electrochemical studies by using a D-optimal mixture design in Design-Expert software revealed an optimized composition of 60% graphite, 14.2% paraffin, 10.8% MWCNT and 15% IL. The optimal modified CPE shows good electrochemical properties that are well matched with model prediction parameters. In the next step, the optimized CPE was modified with gold nanostructures by applying a double-pulse electrochemical technique. The resulting electrode was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and electrochemical impedance spectroscopy. It gives three sharp and well-separated oxidation peaks for ascorbic acid (AA), dopamine (DA), and uric acid (UA). The sensor enables simultaneous determination of AA, DA and UA with linear responses from 0.3 to 285, 0.08 to 200, and 0.1 to 450 μM, respectively, and with 120, 30 and 30 nM detection limits (at an S/N of 3). The method was successfully applied to the determination of AA, DA, and UA in spiked samples of human serum and urine.