Nano sensors with high sensitivity utilize electrical, optical, and acoustic properties to improve the detection limits of analyses. The unique and exceptional properties of nanomaterials are exploited for sensing purposes. High-sensitivity in analyse recognition is achieved by pre-processing of samples, signal amplification and by applying different transduction approaches. In this review, types of signals produced and amplified by Nano sensors are presented, to sense exceptionally small concentrations of analyses present in a sample. The use of such Nano sensors, sensitivity and selectivity can offer different advantages in biomedical applications like earlier detection of disease, toxins or biological threats and create significant improvements in clinical as well as environmental and industrial outcomes Sensors can be classified either based on signal production or by the different methods they employ for signal transduction. Transduction can take place through a number of approaches. There are presently three main transduction approaches categorized based on detection mechanisms electrochemical detection, optical detection and acoustic/mechanical detection. On the other hand, there is constant progress in designing and optimizing new detection mechanisms of transducers to fabricate new types of sensors. There are different subtypes based on the principle of three main transduction approaches. A number of transduction systems are available in combination with other techniques. In the following, we give a brief description of the detection systems that are currently available.

Electrochemical sensors can be used for numerous analyses. Electrical recognition is a quickly expanding field with built up, basic and minimal effort in the manufacturing procedures. At present, there are numerous proposed and marketed gadgets in light of the electrochemical approach including those for pathogens, and toxins the standard principle of electrochemical Nano sensors is a chemical reaction in which electron release, accept or consume ions. This chemical reaction takes place between a restrained ligand and analyse of interest that measurably affect the transduced signal, such as an electrical current or potential. This electrochemical signal is directly quantified and related to the presence of marker of interest/analyse in the sample solution. 

Optical signal detection by Nano sensors provides high sensitivity as a result of the distinctive connections of active sites of nanomaterials with light signals. However, sensitivity is strongly depending on the detection mode of the optical phenomena.  Mechanical detection systems based on nanoparticles allow ultrasensitive detection and measure the changes in mechanical forces at the molecular level. Nano mechanical sensors detect forces, displacements and mass changes. The main advantage is that these sensors are sensitive to mass. Their property to measure the mass renders them versatile since nearly anything has a mass. Determination of mass by mechanical devices is directly related to overall device mass. Therefore mass detection greatly increases when the mass of mechanical sensors decreases to the nanoscale.

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Highly sensitive Nano sensors provide unique signal detection and amplification strategies to push the limits of detection to concentrations. Such sensing capabilities can be extremely useful to detect biomarkers and to diagnose diseases early on or reoccurrence after a treatment. Examples for Nano sensor use include the detection of DNA damage, cancer, virus infections, cardiovascular diseases or Alzheimer disease. However, in many cases the usefulness of Nano sensors has yet to be proven in a clinical setting or even in clinically relevant samples. For electrical detection, high salt concentrations are usually interfering with the measurement.

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Sarah rose
Associate Editor
Nanotechnology Letters