Amperometric lactate nanobiosensor based on reduced graphene oxide, carbon nanotube and gold nanoparticle nanocomposite.

A sensitive amperometric method is reported for the determination of lactate. A platinum electrode was modified with a composite prepared from reduced graphene oxide (rGO), carbon nanotubes (CNTs) and gold nanoparticles. The composite was synthesized by the in-situ reduction of gold(III) ions on the GO-CNT hybrid. Triple composite components showed synergistic effects on the enzyme loading, electrocatalytic activity and electron transfer between receptor and electrode surface. The amperometric lactate sensor was obtained by immobilization of lactate oxidase (LOx) on the modified electrode. LOx catalyzes the conversion of lactate into pyruvate and hydrogen peroxide. The generated hydrogen peroxide is simultaneously involved in the oxidation reaction, which is associated with the electron production. These electrons act as amperometric signal generators. At the low potential of 0.2 V, the nanobiosensor shows a relatively wide linear analytical range (i.e., 0.05-100 mM of lactate) with high electrochemical sensitivity (35.3 µA mM-1 cm-2) and limit of detection of 2.3 µM. The sensor is stable, repeatable and reproducible. It is a highly sensitive tool for the detection of lactate in biological samples under both normoxic and hypoxic conditions. Graphical abstract Schematic representation of an electrochemical biosensor for sensitive detection of lactate in biological and food samples based on reduced graphene oxide-carbon nanotube-gold nanocomposite, as a surface modifier, and lactate oxidase, as a bioreceptor.

Optical assays based on colloidal inorganic nanoparticles.

Colloidal inorganic nanoparticles have wide applications in the detection of analytes and in biological assays. A large number of these assays rely on the ability of gold nanoparticles (AuNPs, in the 20 nm diameter size range) to undergo a color change from red to blue upon aggregation. AuNP assays can be based on cross-linking, non-cross linking or unmodified charge-based aggregation. Nucleic acid-based probes, monoclonal antibodies, and molecular-affinity agents can be attached by covalent or non-covalent means. Surface plasmon resonance and SERS techniques can be utilized. Silver NPs also have attractive optical properties (higher extinction coefficient). Combinations of AuNPs and AgNPs in nanocomposites can have additional advantages. Magnetic NPs and ZnO, TiO2 and ZnS as well as insulator NPs including SiO2 can be employed in colorimetric assays, and some can act as peroxidase mimics in catalytic applications. This review covers the synthesis and stabilization of inorganic NPs and their diverse applications in colorimetric and optical assays for analytes related to environmental contamination (metal ions and pesticides), and for early diagnosis and monitoring of diseases, using medically important biomarkers.

Computational modeling to determine key regulators of hypoxia effects on the lactate production in the glycolysis pathway.

In solid tumors, hypoxia can trigger aberrant expression of transcription factors and genes, resulting in abnormal biological functions such as altered energetic pathways in cancer cells. Glucose metabolism is an important part of this phenomenon, which is associated with changes in the functional expression of transporters and enzymes involved in the glycolysis pathway. The latter phenomenon can finally lead to the lactate accumulation and pH dysregulation in the tumor microenvironment and subsequently further invasion and metastasis of cancer cells. Having capitalized on the computational modeling, in this study, for the first time, we aimed to investigate the effects of hypoxia-induced factor-1 (HIF-1) mediated hypoxia on the magnitude of functional expression of all the enzymes and transporters involved in the glycolysis process. The main objective was to establish a quantitative relationship between the hypoxia intensity and the intracellular lactate levels and determine the key regulators of the glycolysis pathway. This model clearly showed an increase in the lactate concentration during the oxygen depletion. The proposed model also predicted that the phosphofructokinase-1 and phosphoglucomutase enzymes might play the most important roles in the regulation of the lactate production.