Microneedle-based biosensor for minimally-invasive lactate detection

Here we report the first mediated microneedles-based biosensor for minimally invasive continuous sensing of lactate in the dermal interstitial fluid (ISF). To further demonstrate the capability of microneedle arrays as second generation biosensors we have functionalized gold microneedles with nanocarbons at which mediated electron transfer of lactate oxidase takes place. In particular the gold surface of the microneedles electrode has been modified in 3 subsequent steps: i) electrodeposition of Au-multiwalled carbon nanotubes (MWCNTs); ii) electropolymerization of the mediator, methylene blue (MB); iii) immobilization of the enzyme lactate oxidase (LOX) by drop-casting procedure. The resulting microneedle-based LOX biosensor displays an interference-free lactate detection without compromising its sensitivity, stability, selectivity and response time. The performance of the microneedle array, second generation biosensor for lactate detection was assessed in artificial interstitial fluid and in human serum, both spiked with lactate. The results reveal that the new mi- croneedles lactate sensor holds interesting promise for the development of a real-time monitoring device to be used in sport medicine and clinical care

Minimally Invasive Glucose Monitoring Using a Highly Porous Gold Microneedles-Based Biosensor: Characterization and Application in Artificial Interstitial Fluid

In this paper, we present the first highly porous gold (h-PG) microneedles-based second-generation biosensor for minimally invasive monitoring of glucose in artificial interstitial fluid (ISF). A highly porous microneedles-based electrode was prepared by a simple electrochemical self-templating method that involves two steps, gold electrodeposition and hydrogen bubbling at the electrode, which were realized by applying a potential of −2 V versus a saturated calomel electrode (SCE). The highly porous gold surface of the microneedles was modified by immobilization of 6-(ferrocenyl)hexanethiol (FcSH) as a redox mediator and subsequently by immobilization of a flavin adenine dinucleotide glucose dehydrogenase (FAD-GDH) enzyme using a drop-casting method. The microneedles-based FcSH/FAD-GDH biosensor allows for the detection of glucose in artificial interstitial fluid with an extended linear range (0.1–10 mM), high sensitivity (50.86 µA cm−2 mM−1), stability (20% signal loss after 30 days), selectivity (only ascorbic acid showed a response about 10% of glucose signal), and a short response time (3 s). These properties were favourably compared to other microneedles-based glucose biosensors reported in the literature. Finally, the microneedle-arrays-based second-generation biosensor for glucose detection was tested in artificial interstitial fluid opportunely spiked with different concentrations of glucose (simulating healthy physiological conditions while fasting and after lunch) and by placing the electrode into a simulated chitosan/agarose hydrogel skin model embedded in the artificial ISF (continuous glucose monitoring). The obtained current signals had a lag-time of about 2 min compared to the experiments in solution, but they fit perfectly into the linearity range of the biosensor (0.1–10 mM). These promising results show that the proposed h-PG microneedles-based sensor could be used as a wearable, disposable, user-friendly, and automated diagnostic tool for diabetes patients

A general method for the electrochemical evaluation of the bimolecular rate constant in enzyme catalyzed reaction kinetics

A general working curve in terms of the ratio of the kinetic limiting current of bioelectrocatalysis to the diffusion-controlled current recorded in the absence of the enzyme reaction versus the k[E] (k=bimolecular rate constant, [E]=enzyme concentration) group at high concentration of the substrate and at very low mediator concentration was constructed. The curve allows one to evaluate the bimolecular catalytic constant for one- or two-electron mediator from voltammetric data recorded at a fixed scan rate

The use of cyclic voltammetric measurements for the determination of kinetic constants in enzyme-based electrocatalysis. The case of the redox mediated dihydronicotinamide adenine dinucleotide oxidation catalysed by flavoproteins

On the basis of simulated voltammetric curves used as testing data, practical methods to extract the bimolecular rate constant for a mediated enzymatic catalysis with an excess of the substrate are examined. The evaluation criteria are the simplicity of treatment and the agreement between the expected and the obtained values of the rate constants. The results obtained indicate that the different approaches examined are equivalent

A third generation glucose biosensor based on cellobiose dehydrogenase immobilized on a glassy carbon electrode decorated with electrodeposited gold nanoparticles: Characterization and application in human saliva

Efficient direct electron transfer (DET) between a cellobiose dehydrogenase mutant from Corynascus thermophilus (CtCDH C291Y) and a novel glassy carbon (GC)-modified electrode, obtained by direct electrodeposition of gold nanoparticles (AuNPs) was realized. The electrode was further modified with a mixed self-assembled monolayer of 4-aminothiophenol (4-APh) and 4-mercaptobenzoic acid (4-MBA), by using glutaraldehyde (GA) as cross-linking agent. The CtCDH C291Y/GA/4-APh,4-MBA/AuNPs/GC platform showed an apparent heterogeneous electron transfer rate constant (ks) of 19.4 ± 0.6 s−1, with an enhanced theoretical and real enzyme surface coverage (Γtheor and Γreal) of 5287 ± 152 pmol cm−2 and 27 ± 2 pmol cm−2, respectively. The modified electrode was successively used as glucose biosensor exhibiting a detection limit of 6.2 μM, an extended linear range from 0.02 to 30 mM, a sensitivity of 3.1 ± 0.1 μA mM−1 cm−2 (R2 = 0.995), excellent stability and good selectivity. These performances compared favourably with other glucose biosensors reported in the literature. Finally, the biosensor was tested to quantify the glucose content in human saliva samples with successful results in terms of both recovery and correlation with glucose blood levels, allowing further considerations on the development of non-invasive glucose monitoring devices

Untargeted and targeted methodologies in the study of tea (Camellia sinensis L.)

The chemical composition of tea beverage is very complex and not yet completely elucidated. Many factors contribute to the chemical complexity of tea, from plant growth conditions (soil, climate, growth altitude and agricultural practices) and manufacturing processes (drying, steaming, fermentation and storage), to preparation methods (quality of water, infusion time and, not least, the time between tea preparation and consumption). Besides primary metabolites, tea leaves contain a number of secondary metabolites, belonging to many different classes of compounds (such as polyphenols, xanthines, proteic and nonproteic amino acids, sugars, volatile compounds) that are extracted during the infusion and transferred into the beverage. Epidemiological studies have suggested that tea consumption is inversely associated with the risk of developing chronic diseases such as cardiovascular diseases, stroke, some forms of cancer and diabetes. Thus, increasing interest in the health properties of tea resulted in a significant rise in scientific investigation on tea chemical composition. This review article highlights the recent results obtained in the tea beverage characterization using different analytical methodologies. The analytical approaches have been subdivided into two groups: targeted chromatographic and NMR techniques and untargeted NMR analytical approaches. Several examples of untargeted chromatographic techniques coupled with mass spectrometry methodologies are also reported. Advantages, drawbacks and significant applications of the different analytical approaches are discussed