  We present the design, fabrication and characterization of high-\emph{Q}
(\emph{Q}=36,000) polymeric photonic crystal nanobeam cavities made of two
polymers that have an ultra-low index contrast (ratio=1.15) and observed
thermo-optical bistability at hundred microwatt power level. Due to the
extended evanescent field and small mode volumes, polymeric nanobeam cavities
are ideal platform for ultra-sensitive biochemical sensing. We demonstrate that
these sensors have figures of merit (FOM=9190) two orders of magnitude greater
than surface plasmon resonance based sensors, and outperform the commercial
Biacore$^{\mathrm{TM}}$ sensors. The demonstration of high-Q cavity in
low-index-contrast polymers can open up versatile applications using a broad
range of functional and flexible polymeric materials.
