An Integrated Needle-Type Biosensor for Intravascular Glucose and Lactate Monitoring

Microscale Biosensor Array Based on Flexible Polymeric Platform toward Lab-on-a-Needle: Real-Time Multiparameter Biomedical Assays on Curved Needle Surfaces

In vivo sensing of various physical/chemical parameters is gaining increased attention for early prediction and management of various diseases. However, there are major limitations on the fabrication method of multiparameter needle-based in vivo sensing devices, particularly concerning the uniformity between sensors. To address these challenges, we developed a microscale biosensor array for the measurement of electrical conductivity, pH, glucose, and lactate concentrations on a flexible polymeric polyimide platform with electrodeposited electrochemically active layers. The biosensor array was then transferred to a medical needle toward multiparametric in vivo sensing. The flexibility of the sensor platform allowed an easy integration to the curved surface (φ = 1.2 mm) of the needle. Furthermore, the electrodeposition process was used to localize various active materials for corresponding electrochemical sensors on the microscale electrodes with a high precision (patterning area = 150 μm × 2 mm). The biosensor array-modified needle was aimed to discriminate cancer from normal tissues by providing real-time discrimination of glucose, lactate concentration, pH, and electrical conductivity changes associated with the cancer-specific metabolic processes. The sensor performance was thus evaluated using solution samples, covering the physiological concentrations for cancer discrimination. Finally, the possibility of in vivo electrochemical biosensing during needle insertion was confirmed by utilizing the needle in a hydrogel phantom that mimicked the normal and cancer microenvironments.

Simple Fabrication of Flexible Biosensor Arrays Using Direct Writing for Multianalyte Measurement from Human Astrocytes

Simultaneous measurements of glucose, lactate, and neurotransmitters (e.g., glutamate) in cell culture over hours and days can provide a more dynamic and longitudinal perspective on ways neural cells respond to various drugs and environmental cues. Compared with conventional microfabrication techniques, direct writing of conductive ink is cheaper, faster, and customizable, which allows rapid iteration for different applications. Using a simple direct writing technique, we printed biosensor arrays onto cell culture dishes, flexible laminate, and glass to enable multianalyte monitoring. The ink was a composite of PEDOT:PSS conductive polymer, silicone, activated carbon, and Pt microparticles. We applied 0.5% Nafion to the biosensors for selectivity and functionalized them with oxidase enzymes. We characterized biosensors in phosphate-buffered saline and in cell culture medium supplemented with fetal bovine serum. The biosensor arrays measured glucose, lactate, and glutamate simultaneously and continued to function after incubation in cell culture at 37 °C for up to 2 days. We cultured primary human astrocytes on top of the biosensor arrays and placed arrays into astrocyte cultures. The biosensors simultaneously measured glucose, glutamate, and lactate from astrocyte cultures. Direct writing can be integrated with microfluidic organ-on-a-chip platforms or as part of a smart culture dish system. Because we print extrudable and flexible components, sensing elements can be printed on any 3D or flexible substrate.

Lactate and glucose measurement in subepidermal tissue using minimally invasive microperfusion needle

Knowing the concentrations of biological substances can help ascertain physiological and pathological states. In the present study, a minimally invasive microperfusion needle was developed for measuring the concentrations of biological substances in subepidermal tissue. The microperfusion needle has a flow channel with a perforated membrane through which biological substances from subepidermal tissue are extracted. Since this device uses a thin steel acupuncture needle as the base substrate, it has sufficient rigidity for insertion through the skin. The efficacy of the needle was examined by measuring lactate and glucose concentrations in mice. Lactate was injected intraperitoneally, and changes in lactate concentrations in subepidermal tissue over time were measured using the device. Lactate concentrations of blood were also measured as a reference. Lactate was successfully collected using the microperfusion needle, and the lactate concentration of perfused saline was significantly correlated with blood lactate concentration. Glucose solution was administered orally, and the glucose concentration of perfused saline was also correlated with blood glucose concentration. The newly developed microperfusion needle can be used for minimally invasive monitoring of the concentrations of biological substances.

Measurement of subcutaneous biological substances using thin metal needle with micro flow channel

Concentrations of biological substances are useful as indicators of physiological and pathological states. In order to monitor biological substances in daily life, we developed a minimally invasive needle type device with which biological substances are extracted through a microperfusion system inserted under the skin. The perfusion needle has a flow channel with perforated membrane through which biological substances from subepidermal tissue are extracted. The efficacy of the device was examined by measuring lactate concentration of exercising mice. Lactate was successfully collected from the back skin of the mice running on a treadmill using a fabricated microperfusion needle. Lactate concentration of perfused solution correlated with blood lactate concentration.

Simultaneous microchip enzymatic measurements of blood lactate and glucose

A miniaturized capillary electrophoretic (CE) microchip device for the simultaneous measurements of lactate and glucose is described. The new microchip bioassay protocol integrates an electrophoretic separation of lactate and glucose, post-column enzymatic reactions of these metabolites with their respective oxidase enzymes, and an amperometric (anodic) detection of enzymatically-liberated hydrogen peroxide at a gold-coated thick-film carbon detector. Factors influencing the response have been examined and optimized, and the analytical performance has been characterized. Applicability of the microchip assay to clinical samples, such as serum and blood, is demonstrated. The microchip protocol obviates cross enzymatic reactions and interferences from major oxidizable constituents common to dual glucose-lactate enzyme electrodes. Such ability to rapidly separate and quantitate lactate and glucose on a small microchip platform should find important clinical and biotechnological applications.

Microscopic and voltammetric characterization of bioanalytical platforms based on lactate oxidase

A microscopic and voltammetric characterization of lactate oxidase- (LOx-) based bioanalytical platforms for biosensor applications is presented. In this context, emphasis is placed on amperometric biosensors based on LOx that have been immobilized by direct absorption on carbon surfaces, in particular, glassy carbon (GC) and highly ordered pyrolytic graphite (HOPG). The immobilized LOx layers have been characterized using atomic force microscopy (AFM) under liquid conditions and cyclic voltammetry. In addition, spatially resolved mapping of enzymatic activity has been carried out using scanning electrochemical microscopy (SECM). In the presence of lactate with hydroxymethylferrocene (HMF) as a redox mediator in solution, biosensors obtained by direct adsorption of LOx onto GC electrodes exhibited a clear electrocatalytic activity, and lactate could be determined amperometrically at 300 mV versus SSCE. The proposed biosensor also exhibits good operating performance in terms of linearity, detection limit, and lifetime.

A biosensor for the determination of amylase activity

A new biosensing flow injection method for the determination of alpha-amylase activity has been introduced. The method is based on the analysis of maltose produced during the hydrolysis of starch in the presence of alpha-amylase. Maltose determination in the flow system was allowed by the application of peroxide electrode equipped with an enzyme membrane. The membrane was obtained by immobilisation of glucose oxidase, alpha-glucosidase and optionally mutarotase on a cellophane, co-crosslinked by gelatin-glutaraldehyde together with bovine serum albumine. alpha-Glucosidase hydrolyses maltose to alpha-D-glucose, which is converted to beta-D-glucose by mutarotase. beta-D-Glucose is then determined via glucose oxidase. The new biosensor has the limit of detection of 50 nmol l(-1) maltose, which means 2 nkat ml(-1) in alpha-amylase activity units, when the reaction time of amylase was 5 min (determined with respect to a signal-to-noise ratio 3:1). When the reaction time of alpha-amylase was 30 min, the limit of detection was 0.5 nkat ml(-1). A linear range of current response was 0.1-3 mmol l(-1) maltose, with a response time of 35s. The biosensor was stable at least two months and retained 70% of its original activity (with mutarotase the stability is decreased to 3 weeks). When the enzyme membrane was stored in a dry state at 4 degrees C in a refrigerator, the lifetime was approximately 6 months (with mutarotase only 3 months).

Simultaneous monitoring of glucose and lactate by an interference and cross-talk free dual electrode amperometric biosensor based on electropolymerized thin films

An interference and cross-talk free dual electrode amperometric biosensor integrated with a microdialysis sampling system is described, for simultaneous monitoring of glucose and lactate by flow injection analysis. The biosensor is based on a conventional thin layer flow-through cell equipped with a Pt dual electrode (parallel configuration). Each Pt disk was modified by a composite bilayer consisting of an electrosynthesised overoxidized polypyrrole (PPYox) anti-interference membrane covered by an enzyme entrapping gel, obtained by glutaraldehyde co-crosslinking of glucose oxidase or lactate oxidase with bovine serum albumin. The advantages of covalent immobilization techniques were coupled with the excellent interference-rejection capabilities of PPYox. Ascorbate, cysteine, urate and paracetamol produced lactate or glucose bias in the low micromolar range; their responses were, however, completely suppressed when the sample was injected through the microdialysis unit. Under these operational conditions the flow injection responses for glucose and lactate were linear up to 100 and 20 mM with typical sensitivities of 9.9 (+/- 0.1) and 7.2 (+/- 0.1) nA/mM. respectively. The shelf-lifetime of the biosensor was at least 2 months. The potential of the described biosensor was demonstrated by the simultaneous determination of lactate and glucose in untreated tomato juice samples; results were in good agreement with those of a reference method.

Needle-type dual microsensor for the simultaneous monitoring of glucose and insulin

A miniature needle-type sensor suitable for the simultaneous amperometric monitoring of glucose and insulin is described. The integrated microsensor consists of dual (biologically and chemically) modified carbon-paste working electrodes inserted into a 14-guage needle. The glucose probe is based on the biocatalytic action of glucose oxidase, and the insulin one relies on the electrocatalytic activity of ruthenium oxide. The analytical performance of the dual sensor is assessed under flow injection conditions. The needle dual detector exhibits a very rapid response to dynamic changes in the concentrations of glucose and insulin. No apparent cross reactivity is observed in mixtures containing millimolar glucose levels and nanomolar insulin concentrations. The response is highly linear (to at least 1000 nM insulin and 14 mM glucose) and reproducible (RSD = 2.6-4.1%). The combination microsensor holds great promise for real-time measurements of the insulin/glucose ratio and for improved management of diabetes.

Biomolecule immobilization on electrode surfaces by entrapment or attachment to electrochemically polymerized films. A review

The concept and potentialities of electrochemical procedures of biomolecule immobilization based on electropolymerized films are described. The biomolecule entrapment in conventional electrogenerated polymers such as polypyrrole, polyaniline or polyphenol is compared with an electrochemical procedure involving the adsorption of amphiphilic monomers and biomolecules before the polymerization step. Examples of organic phase enzyme electrode and electrical wiring of immobilized enzymes are presented. Furthermore, the construction of controlled architectures based on spatially segregated multilayers, exhibiting complementary biological activities is described. Then, the use of functionalized polymers bearing functional groups for the covalent binding of biomolecules is reported. Moreover, the attachment of biomolecules to biotinylated polymers through affinity interactions based on avidin-biotin bridge is presented.