A cyclodextrin-based approach for selective detection of catecholamine hormone mixtures

Innovative electrochemical platform for the simultaneous determination of L-DOPA and L-tyrosine using layer-by-layer assembled L-proline-linked nanodiamonds on printed graphene

Discovering alternative analytical techniques is crucial for practical applications; thus, this work aims to develop an innovative and simple electrochemical sensor for melanoma and the clinical diagnosis of related disorders by the simultaneous determination of 3,4-dihydroxy-L-phenylalanine (L-DOPA) and L-tyrosine (L-Tyr). The fabrication is based on the layer-by-layer electrodeposition of poly L-proline (poly(L-pro)) and nanodiamond (ND) onto a screen-printed graphene electrode (SPGE). The poly(L-pro)/ND/SPGEs were morphologically characterized by scanning electron microscopy, energy-dispersive X-ray spectrometry, and Raman spectroscopy followed by electrochemical investigation using cyclic voltammetry, differential pulse voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. These modifier-based electrodes pave a feasible way to unlock the coexisting interfering substances from screen-printing ink composition and improve the sensitivity. Additionally, computational chemistry calculations were performed to fully comprehend the sensing behavior on both target analytes. Under optimal conditions, the developed sensor provided linear concentration ranges of 0.075-50 μM, with a detection limit of 0.021 μM for L-DOPA, and 2.5-120 μM with a detection limit of 0.74 μM for L-Tyr. To demonstrate the reliability of the poly(L-pro)/ND/SPGE in practical application, it was successfully applied to the determination of these analytes in human urine and blood serum samples, with satisfactory recovery ranges (81.73-110.62% for L-DOPA and 82.17-110.01% for L-Tyr) and relative standard deviations (0.69-9.90% for L-DOPA and 0.40-9.55% for L-Tyr). Due to its simplicity, long-term stability (> 87.8% of their initial currents after 35 days), and portability, the developed sensor is a promising alternative analytical method for on-site clinical monitoring.

Electrochemical Assay for Extremely Selective Recognition of Fructose Based on 4-Ferrocene-Phenylboronic Acid Probe and β-Cyclodextrins Supramolecular Complex

The aim of the present paper is to highlight a novel electrochemical assay for an extremely-selective detection of fructose thanks to the use of a supramolecular complex between β-cyclodextrins (β-CDs) and a chemically modified ferrocene with boronic acid named 4-Fc-PB/natural-β-CDs. Another kind of β-CDs, the 4-Fc-PB/3-phenylboronic-β-CDs, is proposed for the detection of glucose. The novel electrochemical probe is fully characterized by ¹ H nuclear magnetic resonance, mass spectroscopy, and elemental analysis, while the superior electrochemical performance is assessed in terms of sensitivity and detection limit. The novelty of the present work consists in the role of CDs that for the first time are employed in electrochemistry with a unique detection mechanism based on specific chemical interactions with the target molecule by the introduction of proper binding groups. A highly selective detection of fructose is obtained and it is believed that the proposed mechanism of detection represents a new way to electrochemically sense other molecules by varying the combination of specific groups of the supramolecular complex. The findings are of impactful importance since a quick, easy, cheap, and extremely selective detection of fructose is not yet available in the market, here achieved by using electrochemical methods which are a very growing field.

Study on the Sensing Signal Profiles for Determination of Process Window of Flexible Sensors Based on Surface Treated PDMS/CNT Composite Patches

In this study, analysis of sensing signal profiles was conducted focusing on the close relationship between electrical conductivity and signal intensity in surface treated poly(dimethylsiloxane)/carbon nanotube (PDMS/CNT) composite patches for the purpose of their practical application as flexible chemical sensors. The flexible PDMS/CNT composite patches were prepared from a PDMS/CNT mixture with a two-roll apparatus. It was found that the PDMS/CNT pads showed a high electrical conductivity (10⁻¹ S/m) even at low CNT loading (0.6 wt %) and a contact angle range of 105–118°. The surface of the obtained PDMS/CNT composite patches was treated using a simple bio-conjugation method to incorporate beta-cyclodextrin (beta-CD) molecules onto the surface as a sensing medium, in order to detect a model compound (Methyl Paraben, MePRB). FT-IR spectra indicated that beta-cyclodextrin molecules were effectively introduced on the surface of the PDMS/CNT patches. It was shown that the sensor signal intensity was substantially dependent on the base current value, which increased with increasing CNT loading. Accordingly, the base current value was intimately associated with the electrical conductivity of the composite patches. On the other hand, the increase in current over the base current (ΔI/I₀) obtained after the addition of the model compound was inversely proportional to the CNT content. In this way, analysis on the sensing signal profiles of the flexible chemical sensor system was conducted to determine a process window. This study is a very useful springboard for future research activities, as more profound studies are necessary to fully understand sensing signal profiles.

Smart material platforms for miniaturized devices: implications in disease models and diagnostics

Smart materials are responsive to multiple stimuli like light, temperature, pH and redox reactions with specific changes in state. Various functionalities in miniaturised devices can be achieved through the application of "smart materials" that respond to changes in their surroundings. The change in state of the materials in the presence of a stimulus may be used for on demand alteration of flow patterns in devices, acting as microvalves, as scaffolds for cellular aggregation or as modalities for signal amplification. In this review, we discuss the concepts of smart trigger responsive materials and their applications in miniaturized devices both for organ-on-a-chip disease models and for point-of-care diagnostics. The emphasis is on leveraging the smartness of these materials for example, to allow on demand sample actuation, ion dependent spheroid models for cancer or light dependent contractility of muscle films for organ-on-a-chip applications. The review throws light on the current status, scope for technological enhancements, challenges for translation and future prospects of increased incorporation of smart materials as integral parts of miniaturized devices.

Electrical release of dopamine and levodopa mediated by amphiphilic β-cyclodextrins immobilized on polycrystalline gold

Vesicles of cationic amphiphilic β-cyclodextrins have been immobilized on polycrystalline gold by exploiting the chemical affinity between their amino groups and Au atoms. The presence of cyclodextrins has been widely investigated by means of AFM, XPS, kelvin probe and electrochemical measurements. This multi-functional coating confers distinct electrochemical features such as pH-dependent behavior and partial/total blocking properties towards electro-active species. The host-guest properties of β-cyclodextrins have been successfully exploited in order to trap drugs, like dopamine and levodopa. The further release of these drugs was successfully achieved by providing specific electrical stimuli. This proof-of-concept led us to fabricate an electronic device (i.e. an organic transistor) capable of dispensing both dopamine and levodopa in aqueous solution.