Biological nanosensors

Nanosensor

A nanosensor is a device that makes use of the unique properties of nanomaterials and nanoparticles to detect and measure parameters such as chemical compounds in concentrations as low as one part per billion, or the presence of different infectious agents such as virus or harmful bacteria.

Biosensor

Biosensors represent a rapidly expanding field, at the present time, with an estimated 60% annual growth rate; the major impetus coming from the health-care industry, food quality appraisal and environmental monitoring. Research and development in this field is wide and multidisciplinary. Most of this current endeavour concerns potentiometric and amperometric biosensors and colorimetric paper enzyme strips.

A biosensor is a device or a probe that integrates a biological component, such as a whole bacterium or a biological product (e.g., an enzyme or antibody) with an electronic component to yield a measurable signal and detects, records, and transmits information regarding a physiological change or the presence of various chemical or biological materials in the environment. Biosensors come in a variety of sizes and shapes and can detect and measure concentrations of specific bacteria or hazardous chemicals, measure acidity levels (pH).

Biological nanosensor

Biological nanosensors are used to monitor biomolecular processes such as antibody/antigen interactions, DNA interactions, enzymatic interactions or cellular communication processes, amongst others.

Components

A biological nanosensor is usually composed of (i) a biological recognition system or bioreceptor, such as an antibody, an enzyme, a protein or a DNA strain, and (ii) a transduction mechanism, e.g., an electrochemical detector, an optical transducer, or an amperometric, voltaic or magnetic detector.

Types

There are mainly two subtypes of biological nanosensors based on their working principle: Electrochemical biological nanosensors and photometric biological nanosensors. The electrochemical biological sensors work in a similar way to chemical nanosensors, but in this case, the change in the electronic properties of, for example, a CNT-based FET transistor, is induced either by: (i) A protein or any other chemical composite that binds itself to the functionalized nanotube. (ii) A specific antigen that binds itself to an antibody glued to the nanotube. (iii) A single stranded DNA chain that binds itself to another DNA chain which has been attached to the nanotube. Based on this principle, nanosensors able to detect lung cancer, asthma attacks, different common virus such as the influenza virus, or the parasite responsible for malaria, have been already successfully manufactured. The second subtype of biological nanosensors is based on the use of noble metal nanoparticles and the excitation using optical waves of surface plasmons, i.e., coherent electron waves at the interfaces between these particles. The resonant frequency of the surface plasmons resulting from light irradiation changes when different materials are adsorbed on and in between the particles.

Principle

This technique, known as localized surface plasmon resonance (LPSR), is the underlying principle behind many biological nanosensors. One of the main constraints of this sensing mechanism is the requirement of an external source of light and a device which is able to measure and compare different resonant frequencies of the particles. This can be overcome by means of coordination and communication among nanosensors. For example, nanosensors could locally irradiate the same particles with a much lower power and measure the reradiated energy at different frequencies. The result of this operation could then be processed or forwarded to a data sink.

Nanobiosensor applications

To develop nano biosensors, researchers use carbon nanofibers because they can form an array of tiny electrodes that is even smaller than bacteria and viruses. When these microbial particles are captured at the electrode surface, an electric signal can be detected. This research can be very helpful in the future as it can be applied in the very early stages before an outbreak of disease spreads.Researchers have developed molecular sheaths around the nanotube that respond to a particular chemical and modulate the nanotube's optical properties. They have also developed a layer of olfactory proteins to react with low-concentration odorants for diagnosing diseases at earlier stages. Nanosphere lithography (NSL) derived triangular Ag nanoparticles can be used to detect streptavidin down to one picomolar concentrations and anti-body based piezoelectric nanobiosensor for detection of anthrax and HIV hepatitis.