Photonic Crystals for Biosensing
The emerging threat posed by viruses like influenza, adenovirus and small pox necessitates the development of sensor platforms that can diagnose and detect these pathogens at very low levels and with low false alarm rates. Such systems can enable early stage detection so that the patient can be treated before he/she becomes contagious.
Towards this end I have been working on a sensor platform which combines aspects of nanofluidics, nanophotonics and biomolecular analysis to produce an extremely sensitive sensor design which possesses a low mass limit of detection. Some of the characteristics of a good modern biosensor design are:
- Sufficiently sensitive and specific to detect pre-symptomatic levels of viral RNA and provide subtype information with very low false alarm rates.
- Capable of functioning in liquid (raw sera) environments.
- Provide both target and sample multiplexing capability.
- Reduce the amount of time required for analysis.
- Minimize the number of power consuming components in the entire system.
Optical Biosensors: There are many different classes of biosensor designs, each of which exploit some unique physical phenomena to detect binding events occuring at sensing sites. Optical biosensors are a class of biosensors which exploits light-matter interactions and the phase change that is imparted to the light due to such interactions. The underlying physics is as follows:
In an optical biosensor light is made to interact with some bound biomolecules (usually on the surface of the sensor). The presence of these bound biomolecules increases the local effective refractive index at the surface of the sensor. Since the light experiences this slightly higher effective refractive index due to the bound biomolecular targets at the sensing site it experiences a larger phase change than if the biomolecules had not been bound to the sensor(due to the light experiencing a lower effective refractive index in their absence). Using some clever techniques different optical biosensor designs try to measure this additional iphase change that is imparted due to the presence of bound targets. If they detect a phase change they can infer that they had binding events occuring at the sensing site. In fact in the case of some sensitive optical biosensors it is even possible to quantify the amount of mass bound as a function of the measured phase change in the incident light.
The biggest advantage of optical biosensors over other sensing architectures is that the sensing elements and propagating light do not in any way interfere with the surrounding fluid medium and the bio-chemistry. Thus they are extremely bio-compatible and allow for the possibility of embedding optical sensors in human tissue.
Nanoscale Optofluidic Sensor Arrays (NOSAs):
The NOSA architecture was my attempt at designing a biosensor architecture that would be capable of achieving the 5 goals for a biosensor that are listed above.