Development of photonic crystal biosensor for label free bioassays
Sensitive biosensors are essential to study important biomolecular interactions for diagnostic and drug discovery applications. Measurements of small molecules usually requires labeling with fluorescent tags. The conjugation of these tags, however, may alter or inhibit the functionality of the analyte molecules under study. If inappropriate compounds are selected as drug candidates in the early screening process, it may result in a costly failure later in clinical trials. Thus, label-free methods for performing binding assays in their natural forms have attracted growing attention to obtain accurate molecular binding information. Nevertheless, existing label-free detection techniques have encountered many challenges in achieving sufficiently high sensitivity for real-time detection of small molecule interactions and/or at low concentrations.
We have designed and fabricated a novel label-free biosensor utilizing a unique detection mechanism recently patented by Dr. Ye. A novel open microcavity with a high finesse has been created by using a Photonic Crystal structure in a Total-Internal-Reflection (PC-TIR) configuration. The sensor based on the open microcavity allows label-free measurements of biomolecular interactions in real time, while the high finesse of the cavity ensures ultra-high detection sensitivity. In addition, effective surface chemistry has been utilized to develop efficient biofunctionalization approaches for enhanced selectivity in the label-free bioassays. In this thesis, I have explored two important applications of this novel photonic crystal biosensor. One application is to use the sensor for rapid and sensitive detection of cardiac biomarkers. In current clinical practice, a rise in cardiac troponin I (cTnI) accompanied by ST elevation/depression in electrocardiogram (ECG) is usually diagnostic of myocardial infarction (MI). Although ECG can be easily obtained within minutes at point of patient care, blood testing with conventional approaches is time consuming and becomes a bottleneck for rapid MI diagnosis. The development of our photonic crystal sensor could open up the possibility for signaling a more accurate and timely warning of impending cardiac events at a very early stage. In addition, I demonstrate the wide range of applications of our sensor by utilizing it for detection of anthrax lef gene. Bacillus anthracis has posed a threat of becoming biological weapons of mass destruction due to its virulence factors encoded by the plasmid-borne genes, such as lef for lethal factor. For Anthrax DNA detection, fluorescently labeled DNA probes have long been used to generate the signals. The drawbacks of the fluorescence based biosensing include high cost, background noise, and prolonged operation time required for labeling. The effort to overcome the limits has stimulated the development of label-free biosensing technologies. Surface plasma resonance (SPR) techniques have been developed for Anthrax detection with antibodies, but DNA-based SPR detection of anthrax has not been reported. Our sensor functionalized with a lef probe DNA has been demonstrated as a sensitive and fast approach for Anthrax gene detection, an important application for anti-bioterrorism.