Review on carbon-derived, solid-state, micro and nano sensors for electrochemical sensing applications

The aim of this review is to summarize the most relevant contributions in the development of electrochemical sensors based on carbon materials in the recent years. There have been increasing numbers of reports on the first application of carbon derived materials for the preparation of an electrochemical sensor. These include carbon nanotubes, diamond like carbon films and diamond film-based sensors demonstrating that the particular structure of these carbon material and their unique properties make them a very attractive material for the design of electrochemical biosensors and gas sensors. Carbon nanotubes (CNT) have become one of the most extensively studied nanostructures because of their unique properties. CNT can enhance the electrochemical reactivity of important biomolecules and can promote the electron-transfer reactions of proteins (including those where the redox center is embedded deep within the glycoprotein shell). In addition to enhanced electrochemical reactivity, CNT-modified electrodes have been shown useful to be coated with biomolecules (e.g., nucleic acids) and to alleviate surface fouling effects (such as those involved in the NADH oxidation process). The remarkable sensitivity of CNT conductivity with the surface adsorbates permits the use of CNT as highly sensitive nanoscale sensors. These properties make CNT extremely attractive for a wide range of electrochemical sensors ranging from amperometric enzyme electrodes to DNA hybridization biosensors. Recently, a CNT sensor based fast diagnosis method using non-treated blood assay has been developed for specific detection of hepatitis B virus (HBV) (human liver diseases, such as chronic hepatitis, cirrhosis, and hepatocellular carcinoma caused by hepatitis B virus). The linear detection limits for HBV plasma is in the range 0.5–3.0 μL−1 and for anti- HBVs 0.035–0.242 mg/mL in a 0.1 M NH4H2PO4 electrolyte solution. These detection limits enables early detection of HBV infection in suspected serum samples. Therefore, non-treated blood serum can be directly applied for real-time sensitive detection in medical diagnosis as well as in direct in vivo monitoring. Synthetic diamond has been recognized as an extremely attractive material for both (bio-) chemical sensing and as an interface to biological systems. Synthetic diamond have outstanding electrochemical properties, superior chemical inertness and biocompatibility. Recent advances in the synthesis of highly conducting nanocrystalline-diamond thin films and nano wires have lead to an entirely new class of electrochemical biosensors and bio-inorganic interfaces. In addition, it also combines with development of new chemical approaches to covalently attach biomolecules on the diamond surface also contributed to the advancement of diamond-based biosensors. The feasibility of a capacitive field-effect EDIS (electrolyte-diamond-insulatorsemiconductor) platform for multi-parameter sensing is demonstrated with an O-terminated nanocrystalline-diamond (NCD) film as transducer material for the detection of pH and penicillin concentration. This has also been extended for the label-free electrical monitoring of adsorption and binding of charged macromolecules. One more recent study demonstrated a novel bio-sensing platform, which is introduced by combination of a) geometrically controlled DNA bonding using vertically aligned diamond nano-wires and b) the superior electrochemical sensing properties of diamond as transducer material. Diamond nanowires can be a new approach towards next generation electrochemical gene sensor platforms. This review highlights the advantages of these carbon materials to promote different electron transfer reactions specially those related to biomolecules. Different strategies have been applied for constructing carbon material-based electrochemical sensors, their analytical performance and future prospects are discussed

Multiwalled Carbon Nanotube Biohybrid Based Wearable Sensor

Continuous real-time surveillance of biological markers can have significant implications on disease prognosis. To date, most commercially available continuous monitoring health systems are physical sensors due to the ease of use and non-invasive detection systems. On the other hand, continuous glucose monitoring (CGM) systems that tracks ISF glucose levels are the only commercially available wearable biochemical sensors. These wearable CGM systems significantly improve patients’ diabetes management and prognosis, illustrating that biochemical wearable sensor to monitor other biomarkers, such as lactate, can be highly beneficial. As a product of anaerobic metabolism, blood lactate levels are often used to evaluate health conditions such as endurance capabilities, severe infection, and respiratory failure management of critically ill patients. There are major development and commercialization of blood lactate monitoring systems, but commercially available sensors are hand-held devices that require frequent extraction of blood samples. Thus, there is dire need for a wearable lactate sensor. This thesis presents and investigates the development of wearable carbon nanotube (CNT) based lactate biosensors. A stable enzyme matrix is one of the most important components of biosensors. Covalently linking the enzyme with glutaraldehyde is a common approach but can decrease the enzyme activity. The non-covalent technique relies on using a semi-permeable membrane, such as Nafion, to stabilize the immobilized enzymes. Nafion has been widely used for enzyme immobilization for its high stability and ionic conductivity. Our results demonstrated that the non-covalent approach retained higher enzymatic activity for the glucose sensor compared to the covalent cross-linking technique. Through electrochemical impedance spectroscopy, the 1% Nafion membrane was shown to be stable on for 24 hours. The incorporation of carbon nanotubes in biotransducers have improved sensors’ sensitivity due to their high aspect ratio and ballistic electrical conduction due to the sp2 hybridized carbon. However, many CNT sensor designs fail to take full advantage of the CNTs’ high surface area by placing the CNTs between the enzymes and electrode, squandering a significant portion of conductive surface area that can be used to transmit signals. The multiwalled carbon nanotube (MWNT) used was grown through chemical vapor deposition and had an average diameter and length of 8.28 nm and 150 µm, respectively. Unlike commercially available MWNTs that require purification in acidic solution which consequently introduced defects, the MWNT forest was pristine and preserved the electrical properties. The MWNT was coated with chitosan (CHIT) to improve solubility and integrated in the enzyme matrix to create a porous 3D CNT-enzyme matrix. Our results show that the CNT integrated enzyme matrix slightly increased in sensitivity. The fabrication of a conductive and hydrophilic matrix depends on the optimal ratio of CNT to CHIT and CNT-CHIT to LOx. Lastly, we developed a wearable microneedle platform that consists of a hollow microneedle array, polydimethylsiloxane (PDMS) chamber, and sensor strip. The platform utilizes a pressure-driven convection technique by designing a pumping mechanism on the top of the PDMS chamber. The platform successfully extracted up to 500 µL of solution with a viscosity comparable to blood. This study investigates the development of biochemical sensors for continuous monitoring. Our 3D CNT-enzymatic matrix offers new insights and approaches to produce stable and sensitive sensors towards the actualization of wearable biochemical sensors

Emerging (Bio)Sensing Technology for Assessing and Monitoring Freshwater Contamination - Methods and Applications

Ecological Water Quality - Water Treatment and ReuseWater is life and its preservation is not only a moral obligation but also a legal requirement. By 2030, global demands will exceed more than 40 % the existing resources and more than a third of the world's population will have to deal with water shortages (European Environmental Agency [EEA], 2010). Climate change effects on water resources will not help. Efforts are being made throughout Europe towards a reduced and efficient water use and prevention of any further deterioration of the quality of water (Eurostat, European Comission [EC], 2010). The Water Framework Directive (EC, 2000) lays down provisions for monitoring, assessing and classifying water quality. Supporting this, the Drinking Water sets standards for 48 microbiological and chemical parameters that must be monitored and tested regularly (EC, 1998). The Bathing Water Directive also sets concentration limits for microbiological pollutants in inland and coastal bathing waters (EC, 2006), addressing risks from algae and cyanobacteria contamination and faecal contamination, requiring immediate action, including the provision of information to the public, to prevent exposure. With these directives, among others, the European Union [EU] expects to offer its citizens, by 2015, fresh and coastal waters of good quality