Advances in carbon nanotube based electrochemical sensors for bioanalytical applications

Abstract

Electrochemical (EC) sensing approaches have exploited the use of carbon nanotubes (CNTs) as electrode materials owing to their unique structures and properties to provide strong electrocatalytic activity with minimal surface fouling. Nanofabrication and device integration technologies have emerged along with significant advances in the synthesis, purification, conjugation and biofunctionalization of CNTs. Such combined efforts have contributed towards the rapid development of CNT-based sensors for a plethora of important analytes with improved detection sensitivity and selectivity. The use of CNTs opens an opportunity for the direct electron transfer between the enzyme and the active electrode area. Of particular interest are also excellent electrocatalytic activities of CNTs on the redox reaction of hydrogen peroxide and nicotinamide adenine dinucleotide, two major by-products of enzymatic reactions. This excellent electrocatalysis holds a promising future for the simple design and implementation of on-site biosensors for oxidases and dehydrogenases with enhanced selectivity. To date, the use of an anti-interference layer or an artificial electron mediator is critically needed to circumvent unwanted endogenous electroactive species. Such interfering species are effectively suppressed by using CNT based electrodes since the oxidation of NADH, thiols, hydrogen peroxide, etc. by CNTs can be performed at low potentials. Nevertheless, the major future challenges for the development of CNT-EC sensors include miniaturization, optimization and simplification of the procedure for fabricating CNT based electrodes with minimal non-specific binding, high sensitivity and rapid response followed by their extensive validation using "real world" samples. A high resistance to electrode fouling and selectivity are the two key pending issues for the application of CNT-based biosensors in clinical chemistry, food quality and control, waste water treatment and bioprocessing.

Properties and Customization of Sensor Materials for Biomedical Applications

“…It is perhaps worth noting that the CNTs' electrocatalytic properties are somewhat controversial. In fact, it has been suggested that it is the presence of metal impurities introduced during the preparation of CNTs, rather than the CNTs themselves, that provides the basis of the electrocatalytic behavior (209,240,241). In addition, there is still not unanimous agreement regarding the cytotoxicity of CNTs, although some authors support that functionalization of CNTs can control it (240,241).…”

“…In fact, it has been suggested that it is the presence of metal impurities introduced during the preparation of CNTs, rather than the CNTs themselves, that provides the basis of the electrocatalytic behavior (209,240,241). In addition, there is still not unanimous agreement regarding the cytotoxicity of CNTs, although some authors support that functionalization of CNTs can control it (240,241). Finally, an important aspect to consider is the relatively high cost of producing and purifying CNTs (although this is decreasing over time), which may in some way explain the delay in their uptake by the industry (235,240).…”

“…In addition, there is still not unanimous agreement regarding the cytotoxicity of CNTs, although some authors support that functionalization of CNTs can control it (240,241). Finally, an important aspect to consider is the relatively high cost of producing and purifying CNTs (although this is decreasing over time), which may in some way explain the delay in their uptake by the industry (235,240).…”

“…Nanocomposites are formed by combining nanoscaled-materials in order to obtain synergetic effects (264,265), such as improvements in the sensitivity and LOD of sensors, and to limit biofouling (240). Nanocomposites have been also investigated as a means to create a suitable microenvironment for the stabilization of biomolecules (266).…”

Design, development, and validation of an in-situ biosensor array for metabolite monitoring of cell cultures

“…There are several methods to deposit carbon nanotubes on metal electrodes. Electrodeposition is by far one of the most precise and reliable techniques to deposit carbon nanotubes even on sub-mm electrodes (Vashist et al, 2011). Electrodeposition is a method to arrange macromolecules by applying a voltage on an electrode.…”