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An ultra-sensitive and selective quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor platform was demonstrated for detection of carbon monoxide (CO) and nitrous oxide (N 2 O). This sensor used a stateof-the art 4.61 µm high power, continuous wave (CW), distributed feedback quantum cascade laser (DFB-QCL) operating at 10°C as the excitation source. For the R(6) CO absorption line, located at 2169.2 cm −1 , a minimum detection limit (MDL) of 1.5 parts per billion by volume (ppbv) at atmospheric pressure was achieved with a 1 sec acquisition time and the addition of 2.6% water vapor concentration in the analyzed gas mixture. For the N 2 O detection, a MDL of 23 ppbv was obtained at an optimum gas pressure of 100 Torr and with the same water vapor content of 2.6%. In both cases the presence of water vapor increases the detected CO and N 2 O QEPAS signal levels as a result of enhancing the vibrational-translational relaxation rate of both target gases. Allan deviation analyses were performed to investigate the long term performance of the CO and N 2 O QEPAS sensor systems. For the optimum data acquisition time of 500 sec a MDL of 340 pptv and 4 ppbv was obtained for CO and N 2 O detection, respectively. To demonstrate reliable and robust operation of the QEPAS sensor a continuous monitoring of atmospheric CO and N 2 O concentration levels for a period of 5 hours were performed. 6728-6738 (2003). 27. X. Chao, J. B. Jeffries, and R. K. Hanson, "Wavelength-modulation-spectroscopy for real-time, in situ NO detection in combustion gases with a 5.2 µm quantum-cascade laser," Appl. Phys. B 106(4), 987-997 (2012). 28. L. Dong, R. Lewicki, K. Liu, P. R. Buerki, M. J. Weida, and F. K. Tittel, "Ultra-sensitive carbon monoxide detection by using EC-QCL based quartz-enhanced photoacoustic spectroscopy," Appl. Phys. B 107(2), 275-283 (2012). 29. L. ©2013 Optical Society of America

A gas sensing method based on quartz-tuning-fork enhanced photothermal spectroscopy (QEPTS) is reported in this paper. Unlike usually used thermally sensitive elements, a sharply resonant quartz-tuning-fork with the capability of enhanced mechanical resonance was used to amplify the photothermal signal level. Acetylene (C 2 H 2) detection was used to verify the QEPTS sensor performance. The measured results indicate a minimum detection limit (MDL) of 718 ppb and a normalized noise equivalent absorption coefficient (NNEA) of 7.63 × 10 −9 cm −1 W/√Hz. This performance demonstrates that QEPTS can be an ultra-high sensitive technique for gas detection and shows superiority when compared to usually used methods of tunable diode laser absorption spectroscopy (TDLAS) and quartzenhanced photoacoustic spectroscopy (QEPAS). Furthermore, when compared to an optical detector, especially a costly mercury cadmium telluride (MCT) detector with cryogenic cooling used in TDLAS, a quartz-tuning-fork is much cheap and tiny. Besides, compared to the QEPAS technique, QEPTS is a non-contact measurement technique and therefore can be used for standoff and remote trace gas detection.

Despite increasing demands to employ amphiphilic micelles as nanocarriers and nanoreactors, it remains a significant challenge to simultaneously reduce the particle size and enhance the particle stability. Complementary to covalent chemical bonding and attractive intermolecular interactions, entropic repulsion can be incorporated by rational design in the headgroup of an amphiphile to generate small micelles with enhanced stability. A new family of amphiphilic peptide-polymer conjugates is presented where the hydrophilic headgroup is composed of a 3-helix coiled-coil with poly(ethylene glycol) attached to the exterior of the helix bundle. When micelles form, the PEG chains are confined in close proximity and are compressed to act as a spring to general lateral pressure. The formation of 3-helix bundles determines the location and the directionalities of the force vector of each PEG elastic spring so as to slow down amphiphile desorption. Since each component of the amphiphile can be readily tailored, these micelles provide numerous opportunities to meet current demands for organic nanocarriers with tunable stability in life science and energy science. Furthermore, present studies open new avenues to use energy arising from entropic polymer chain deformation to self-assemble energetically stable single nanoscopic objects, much like repulsion that stabilizes bulk assemblies of colloidal particles.