Nanotechnology offers new options for design of chemical sensors and biosensors due to their unique features including
- Tunable shape and size dependent chemical and physical properties
- Miniaturization and low power requirements for portable and implantable devices
- Multiplexing: Several nanomaterials (e.g. nanoparticles, nanorods, nanowires, core-shell nanospheres) each with unique sensitivity to a specific analyte can be integrated on a single chip like platform
- Nanosensors could be integrated into clothes for wearable, real-time personal sensing devices for environmental monitoring and health monitoring
- Nanomaterials can be used from designing inexpensive portable environmental sensor to single molecule detection inside the cell.
Rapid use of nanomaterials in design of novel biosensor is evident from three recent reports of designing novel sensors for applications as varied as diagnostics, environmental monitoring, and for sensing inside a cell.
Gold Nanoparticles for Detection of Lung Cancer
Most common applications of Gold Nanoparticles for sensing leverage changes in optical properties in response to some binding event. But Hossam Haick at Haifa, Israel uses conducting properties of Gold nanoparticle coated gold film for sensing varieties of organic molecules present in the breath to diagnose Lung Cancer.
Schematic of Chemoresistive sensor based on Gold nanoparticles ().
First, around 300-400 volatile organic compounds (VOCs) were identified in the breath samples using GC-MS (Gas chromatography-Mass spectroscopy). That number was narrowed down to 33 VOCs that were present at different concentrations and in different composition in normal healthy volunteers and Lung cancer patients. Second, nine chemoresistive sensors were fabricated each containing 5nm gold nanoparticles decorated with monolayer of organic thiol molecules. Each sensor responds differently to the presence of panel of 33 VOCs in the breath of the person. The panel of nine sensors was able to diagnose Lung cancer patients simply by analyzing the breath samples.
This sensor architecture can be easily mass produced and has the potential for use in any number of application.
Europium Doped Silica Nanoparticles for Detection of Reactive Oxygen Species (ROS) Inside Cells
The principle behind this sensor , developed by group at CNRS, France, is that silica nanoparticles doped with europium undergo photoreduction under laser irradiation but re-oxidize in the presence of oxidants (e.g. H2O2 etc.), leading to recovery of luminescence. The sensors can detect H2O2 inside a cell and has dynamic range of 1-45micromolar. The sensor can also be regenerated and are capable of time-resolved detection of ROS. These nanoparticles are not toxic to the cells and may be targeted to various cell compartment by appropriate functionalization.
Single Walled Carbon Nanotubes (SWNTs) Sensor for Oxygen Detection
This sensor proposed by the group at University of Pittsburg combines the best of above two sensors. First, a chemoresistive sensor is made by SWNT networks decorated with an oxygen-sensitive Europium containing dendrimer. Second, when this sensor is illuminated with 365 nm light, it shows optical spectroscopic and electrical conductance sensitivity towards oxygen gas at room temperature under ambient pressure. The sensor has linear sensitivity towards oxygen gas in the environmentally relevant concentration range of 5–27%.
These three reports are just a snapshot of large arrays of sensing platforms being designed using nanomaterials. Hopefully, we will soon see a transition of these technologies from research laboratories to the commercial products. Just a reminder though health risk of nanoparticles is of growing concern and will have to be taken into concern before disposable/wearable/bedside nanosensors become a reality