Platinum nanoparticle decorated vertically aligned graphene screen-printed electrodes: electrochemical characterisation and exploration towards the hydrogen evolution reaction.

We present the fabrication of platinum (Pt0) nanoparticle (ca. 3 nm average diameter) decorated vertically aligned graphene (VG) screen-printed electrodes (Pt/VG-SPE) and explore their physicochemical characteristics and electrocatalytic activity towards the hydrogen evolution reaction (HER) in acidic media (0.5 M H2SO4). The Pt/VG-SPEs exhibit remarkable HER activity with an overpotential (recorded at -10 mA cm-2) and Tafel value of 47 mV (vs. RHE) and 27 mV dec-1. These values demonstrate the Pt/VG-SPEs as significantly more electrocatalytic than a bare/unmodified VG-SPE (789 mV (vs. RHE) and 97 mV dec-1). The uniform coverage of Pt0 nanoparticles (ca. 3 nm) upon the VG-SPE support results in a low loading of Pt0 nanoparticles (ca. 4 µg cm-2), yet yields comparable HER activity to optimal Pt based catalysts reported in the literature, with the advantages of being comparatively cheap, highly reproducible and tailorable platforms for HER catalysis. In order to test any potential dissolution of Pt0 from the Pt/VG-SPE surface, which is a key consideration for any HER catalyst, we additively manufactured (AM) a bespoke electrochemical flow cell that allowed for the electrolyte to be collected at regular intervals and analysed via inductively coupled plasma optical emission spectroscopy (ICP-OES). The AM electrochemical cell can be rapidly tailored to a plethora of geometries making it compatible with any size/shape of electrochemical platform. This work presents a novel and highly competitive HER platform and a novel AM technique for exploring the extent of Pt0 nanoparticle dissolution upon the electrode surface, making it an essential study for those seeking to test the stability/catalyst discharge of their given electrochemical platforms.

Chemometric-assisted construction of a biosensing device to measure chlorogenic acid content in brewed coffee beverages to discriminate quality.

In this work we propose the use of statistical mixture design in the construction of a biosensor device based on graphite oxide, platinum nanoparticles and biomaterials obtained from Botryosphaeria rhodina MAMB-05. The biosensor was characterized by electrochemical impedance spectroscopy. Under optimized experimental parameters by factorial design, the biosensor was applied to the voltammetric determination of chlorogenic acid (CGA) measured as 5-O-caffeoylquinic acid (5-CQA). The biosensor response was linear (R2 = 0.998) for 5-CQA in the concentration range 0.56-7.3 µmol L-1, with limit of detection and quantification of 0.18 and 0.59 µmol L-1, respectively. The new biosensing device was applied to quality control analysis based upon the determination of CGA content in specialty and traditional coffee beverages. The results indicated that specialty coffee had a significantly higher content of CGA. Principal component analysis of the voltammetric fingerprint of brewed coffees revealed that the laccase-based biosensor can be used for their discrimination.

Carboxymethyl-botryosphaeran stabilized carbon nanotubes aqueous dispersion: A new platform design for electrochemical sensing of desloratadine.

The polysaccharide carboxymethyl-botryosphaeran (CMB) was used to improve the dispersion of multi-walled carbon nanotubes (MWCNTs) in water. This feature was applied in modifying a glassy carbon electrode (GCE) to construct a sensitive voltammetric sensor for the determination of desloratadine (DESL), a tricyclic antihistamine. The morphology and spectroscopic behavior of the sensor were evaluated. The modified sensor was characterized as homogeneous, and presented a higher electroactive area and a lower charge transfer resistance compared to the unmodified GCE. Using linear sweep voltammetry at 25 mV s-1, the developed sensor presented a sensitivity of 1.018 µA L µmol-1 in the linear working range of 1.99-32.9 µmol L-1, with a detection limit of 0.88 µmol L-1 of DESL in 0.10 mol L-1 potassium hydrogen-phosphate solution (pH 8.0). In addition, the sensor showed excellent repeatability with a relative standard deviation of only 1.02% for a sequence of 10 measurements. The sensor was successfully applied in the analysis of pharmaceutical preparations containing DESL, with equivalent results compared to a validated spectrophotometric method at the 95% confidence level. The sensor was also employed in the analysis of a spiked sample of DESL in rat serum.

Assessment of the performance of triphenylphosphine for the voltammetric determination of elemental sulphur in cosmetic products.

In this paper, an alternative voltammetric method for the determination of elemental sulphur in cosmetic products is presented. It is based on the decrease of triphenylphosphine oxidation current in the presence of elemental sulphur by using a glassy carbon electrode. A solution of 2% (m/v) acetic acid and 0.6 mol L-1 sodium acetate in methanol was used as a supporting electrolyte. The experimental conditions for indirect determination of elemental sulphur were established. Using square-wave voltammetry, the analytical curve was linear in the elemental sulphur concentration range of 9.94-271 µmol L-1, with a detection limit of 2.59 µmol L-1. The method was successfully applied to determine elemental sulphur in soap bars and anti-acne cream, without any preliminary sample treatment, therefore, it is shortened and simplified. The results obtained with the indirect voltammetric method were not statistically different in comparison with a titrimetric one, at a 95% confidence level. Additionally, excellent recovery percentages were obtained, proving no matrix interferences.

Amperometric determination of ascorbic acid with a glassy carbon electrode modified with TiO2-gold nanoparticles integrated into carbon nanotubes.

A glassy carbon electrode was modified with a TiO2-gold nanoparticle hybrid integrated with multi-walled carbon nanotubes in a dihexadecylphosphate film (TiO2-Au NP-MWCNT-DHP/GCE) and applied to amperometric determination of ascorbic acid (AA). The modified sensor displays fast charge transfer and shows an irreversible anodic behavior for AA by cyclic voltammetry. Under optimal experimental conditions and using amperometry at 0.4 V, the analytical curve presented a statistical linear concentration range for AA from 5.0 to 51 µmol L-1, with a limit of detection of 1.2 µmol L-1. The electrode was successfully applied to the determination of AA in pharmaceutical and fruit juice without the need for major pretreatment of samples. Graphical abstract Schematic of a new sensing platform for ascorbic acid (AA). It is based on a glassy carbon electrode (GCE) modified with TiO2-Au nanoparticles integrated into carbon nanotubes in a dihexadecylphosphate film. The sensor was applied to amperometric determination of AA in juice and pharmaceutical samples.