We demonstrate the rapid detection of explosive vapors based on a fiber-based optical Fabry-Pérot (FP) gas sensor. The
sensing probe of the FP sensor is composed of a thin metal layer and a vapor-sensitive polymer layer that are deposited
sequentially on a cleaved fiber endface to form an FP cavity. The interference spectrum generated from the reflected
light at the metal-polymer and polymer-air interfaces changes upon the absorption of gas analyte. By monitoring the
interference shift, we are able to obtain quantitative and knetic information of the interaction between the analyte and the
polymer layer. We further assemble the FP sensor with a short fused silica capillary into a sensor module, and employ it
in a gas chromotgraphy (GC) system for selevtive rapid on-column detection. In this report, we specifically target 2, 4-
dinitrotoluene (DNT) and 2, 4, 6-trinitrotoluene (TNT) for their obvious defense applications. This work could lead to a
portable sensor capable of detecting low concentrations of DNT, TNT, and other explosive chemicals.
Microfluidic lasers, which utilize liquid as a gain medium, are of great interest for lab-on-a-chip devices due to their
small size, tunability, and cost-effectiveness. We demonstrate a soft-lithography-based opto-fluidic ring resonator
(OFRR) laser which can be produced in arrays of identical rings in polydimethyl siloxane (PDMS). The PDMS
structures are produced from a silicon mold fabricated using reactive ion etching (RIE) and are both robust and reusable.
Using rhodamine 6G in a tetraethylene glycol (TEG) dye solvent provides enough refractive index contrast with PDMS
to generate a multimode lasing signal from rings 200 to 400 microns in diameter and lasing thresholds of 2.7 μJ/mm<sup>2</sup>
centered around 580 nm. These rings are coupled to liquid waveguides which conveniently direct the lasing emission to
other on-chip devices. Since the rings and waveguides are not in fluidic contact, many rings may potentially be coupled
into a single waveguide for multi-color emission. Separating the ring and waveguide fluidics also prevents unwanted
absorption of the lasing signal by extra dye molecules.
We demonstrate the utility of the opto-fluidic ring resonator (OFRR) sensor for the purpose of analyzing the degree of
methylation in sample oligonucleotides. Cytosine methylation, a regular epigenetic function in cellular growth and
metabolism, is prone to abnormal behavior that may lead to uncontrolled suppression of key genes involved with cellular
proliferation. Such behavior is suspected to be strongly related to the occurrence of several types of cancers. The OFRR
is demonstrated as a tool to explore and monitor the degree of methylation in DNA. Two different approaches are
explored, using either bisulfite modification or immunoprecipitation. The methods are compared and the signal response
for both methods is characterized.
In this work we present a method for creating an integrated optofluidic ring resonator (OFRR) laser system by
embedding it in a low index polymer, polydimethylsiloxane (PDMS). Packaging the OFRR inside PDMS enhances
portability, mechanical stability, and the ability to connect it to chip-based microfluidics. The OFRR retains high Q-factors
even in the polymer (> 10<sup>6</sup>) and exhibits a low lasing threshold (<1 μJ/mm<sup>2</sup>). Additionally, the laser emission can
be efficiently and directionally coupled out through an optical fiber or fiber prism in touch with the ring resonator. At 2.2
μJ/mm<sup>2</sup> pump intensity, the laser output from the fiber is 80 nW, corresponding to 50% power extraction efficiency. Our
work will lead to novel design in lab-on-a-chip devices and micro total analysis systems for biological and chemical