A versatile biosensor device for continuous biomedical monitoring

Biosensors Incorporating Bimetallic Nanoparticles

This article presents a review of electrochemical bio-sensing for target analytes based on the use of electrocatalytic bimetallic nanoparticles (NPs), which can improve both the sensitivity and selectivity of biosensors. The review moves quickly from an introduction to the field of bio-sensing, to the importance of biosensors in today's society, the nature of the electrochemical methods employed and the attendant problems encountered. The role of electrocatalysts is introduced with reference to the three generations of biosensors. The contributions made by previous workers using bimetallic constructs, grouped by target analyte, are then examined in detail; following which, the synthesis and characterization of the catalytic particles is examined prior to a summary of the current state of endeavor. Finally, some perspectives for the future of bimetallic NPs in biosensors are given.

Microneedle array-based carbon paste amperometric sensors and biosensors

The design and characterization of a microneedle array-based carbon paste electrode towards minimally invasive electrochemical sensing are described. Arrays consisting of 3 × 3 pyramidal microneedle structures, each with an opening of 425 µm, were loaded with a metallized carbon paste transducer. The renewable nature of carbon paste electrodes enables the convenient packing of hollow non-planar microneedles with pastes that contain assorted catalysts and biocatalysts. Smoothing the surface results in good microelectrode-to-microelectrode uniformity. Optical and scanning electron micrographs shed useful insights into the surface morphology at the microneedle apertures. The attractive performance of the novel microneedle electrode arrays is illustrated in vitro for the low-potential detection of hydrogen peroxide at rhodium-dispersed carbon paste microneedles and for lactate biosensing by the inclusion of lactate oxidase in the metallized carbon paste matrix. Highly repeatable sensing is observed following consecutive cycles of packing/unpacking the carbon paste. The operational stability of the array is demonstrated as well as the interference-free detection of lactate in the presence of physiologically relevant levels of ascorbic acid, uric acid, and acetaminophen. Upon addressing the biofouling effects associated with on-body sensing, the microneedle carbon paste platform would be attractive for the subcutaneous electrochemical monitoring of a number of physiologically relevant analytes.

In vivo secretome sampling technology for proteomics

Secretome is a critical mediator for cell-cell and microbe-cell interaction. Identification of secretome will endow researchers with important biomarkers and therapeutic targets as well as reinforce the current methods used in the systems biology research of cell-cell interactions. Here, we introduce an in vivo sampling technique using capillary ultrafiltration (CUF) probes that are capable of continuously collecting pure in vivo secretome from tissue microenvironments. Great benefits of CUF probes when compared with other current sampling techniques have been acknowledged. CUF probes can be designed to fit various in vivo models and they are easily adapted to different protein-detection systems including mass spectrometers. The future challenges and clinical advantages of CUF probe sampling are also highlighted in this review. Many prospective properties such as simple manipulation, dynamic sampling, pathogen clearance, online mass spectrometric coupling, and disease treatment and monitoring have made CUF probes attractive for clinical uses in the near future.

The region ion sensitive field effect transistor, a novel bioelectronic nanosensor

A novel type of bioelectronic region ion sensitive field effect transistor (RISFET) nanosensor was constructed and demonstrated on two different sensor chips that could measure glucose with good linearity in the range of 0-0.6mM and 0-0.3mM with a limit of detection of 0.1 and 0.04 mM, respectively. The sensor is based on the principle of focusing charged reaction products with an electrical field in a region between the sensing electrodes. For glucose measurements, negatively charged gluconate ions were gathered between the sensing electrodes. The signal current response was measured using a low-noise pico ammeter (pA). Two different sizes of the RISFET sensor chips were constructed using conventional electron beam lithography. The measurements are done in partial volumes mainly restricted by the working distance between the sensing electrodes (790 and 2500 nm, respectively) and the influence of electrical fields that are concentrating the ions. The sensitivity was 28 pA/mM (2500 nm) and 830 pA/mM (790 nm), respectively. That is an increase in field strength by five times between the sensing electrodes increased the sensitivity by 30 times. The volumes expressed in this way are in low or sub femtoliter range. Preliminary studies revealed that with suitable modification and control of parameters such as the electric control signals and the chip electrode dimensions this sensor could also be used as a nanobiosensor by applying single enzyme molecule trapping. Hypotheses are given for impedance factors of the RISFET conducting channel.

Electrosynthesized poly(pyrrole)/poly(2-naphthol) bilayer membrane as an effective anti-interference layer for simultaneous determination of acethylcholine and choline by a dual electrode amperometric biosensor

Several neural diseases appear related to the neurotransmitter acethylcholine (ACh) and its metabolite choline (Ch) brain levels so that their simultaneous determination is essential. A cross-talk and interference free dual electrode amperometric biosensor for the simultaneous determination of both analytes has been developed. Acetylcholinesterase (AChE) and choline oxidase (ChO) were immobilized by glutaraldehyde co-crosslinking with bovine serum albumin. A very efficient rejection of electroactive interferents has been achieved by a novel electrosynthesized polymeric bilayer membrane composed by overoxidised poly(pyrrole) and poly(2-naphthol) films. Sensitivities towards several electroactive interferents ranged from ca. 0.04% (e.g. ascorbate) to ca. 0.3% (e.g. dopamine) of those relevant to ACh and Ch (11 and 15 microA/microM, respectively). Detection limits (at S/N=3) in flow injection analysis were ca. 100 nM for both ACh and Ch at the ChO-AChE electrode and ca. 40 nM for Ch at the ChO sensor. Biosensor performances appear more than adequate for brain tissue homogenates and cerebrospinal fluids analysis where average levels in the low micromolar range are typically found.

Implantable chemical sensors for real-time clinical monitoring: progress and challenges

Recently, progress has been made in the development of implantable chemical sensors capable of real-time monitoring of clinically important species such as PO(2), PCO(2), pH, glucose and lactate. The need for developing truly biocompatible materials for sensor fabrication remains the most significant challenge for achieving robust and reliable sensors capable of monitoring the real-time physiological status of patients.

Glucose gradient differences in subcutaneous tissue of healthy volunteers assessed with ultraslow microdialysis and a nanolitre glucose sensor

The abdominal subcutaneous interstitium is easily accessible for monitoring glucose for Diabetes Mellitus research and management. The available glucose sensing devices demand frequent blood sampling by finger pricking for calibration. Moreover, there is controversy about the exact relationship between the levels of glucose in the subcutis and blood. In the present study ultra-slow microdialysis was applied for subcutaneous fluid sampling, allowing continuous measurement of glucose in an equilibrated fluid using a nanolitre size sensor. The present method avoids in vivo calibration. During an oral glucose tolerance test glucose levels were measured simultaneously in blood, in adipose tissue and loose connective tissue layers of the abdominal subcutis in seven healthy subjects. Fasting glucose levels (mM) were 2.52 +/- 0.77 in adipose tissue and 4.67 +/- 0.17 in blood, this difference increasing to 6.40 +/- 1.57 and 11.59 +/- 1.52 at maximal glucose concentration. Moreover, the kinetics of glucose in blood and adipose tissue were different. In contrast, connective tissue glucose levels differed insignificantly (4.71 +/- 0.21 fasting and 11.70 +/- 1.96 at maximum) from those in blood and correlated well (r2 = 0.962). Ultra-slow microdialysis combined with a nanolitre glucose sensor could be of benefit to patients in intensive diabetes therapy. Frequent blood sampling for in vivo calibration can be avoided by monitoring glucose in the abdominal subcutaneous loose connective tissue, rather than in the adipose tissue.