Miniaturized smart sensors that can perform sensitive and selective real-time monitoring of target analytes are tremendously valuable for various sensing applications. We developed selective nanocoatings by combining trinitrotoluene (TNT) receptors bound to conjugated polydiacetylene (PDA) polymers with single-walled carbon nanotube field-effect transistors (SWNT-FET). Selective binding events between the TNT molecules and phage display derived TNT receptors were effectively transduced to sensitive SWNT-FET conductance sensors through the PDA coating layers. The resulting sensors exhibited an unprecedented 1 fM sensitivity toward TNT in real time, with excellent selectivity over various similar aromatic compounds. Our biomimetic receptor coating approach may be useful for the development of sensitive and selective micro- and nanoelectronic sensor devices for various other target analytes.

The photodissociation dynamics of propyne and allene are investigated in two molecular beam/ photodissociation instruments, one using electron impact ionization and the other using tunable vacuum ultraviolet ͑VUV͒ light to photoionize the photoproducts. The primary dissociation channels for both reactants are C 3 H 3 ϩH and C 3 H 2 ϩH 2. Measurement of the photoionization efficiency curves on the VUV instrument shows that the C 3 H 3 product from propyne is the propynyl (CH 3 CC) radical, whereas the C 3 H 3 product from allene is the propargyl (CH 2 CCH) radical. The dominant C 3 H 2 product from both reactants is the propadienylidene (H 2 CCC) radical. We also observe a small amount of secondary C 3 H 2 product from photodissociation of the C 3 H 3 radicals in both cases.

Quantum electrodynamics in the Landau gauge is investigated in a different mann~r from Nakanishi's theory. A dipole ghost field is introduced in another simple way. It is shown that the Landau gauge representation can be obtained by a unitary transformation from the usual Feynman gauge representation. The two representations are equivalent to each other, though photon propagators take different forms superficially in each case. Supplementary conditions to eliminate the ghost states are discussed with the Lorentz condition. It is asserted that the interaction picture in the Landau gauge is also possible. *) Gota and Obara 2 ) investigated a canonical quantization method of the free electromagnetic field in the Landau gauge starting with the same field equations as those in Nakanishi's case. In their quantization the dipole ghost states are not introduced, though the longitudinal and scalar photons have peculiar characters. at Univ of Iowa-Law Library on June 7, 2015 http://ptp.oxfordjournals.org/ Downloaded from *) The q-number gauge transformation of the Green functions for charged particles was investigated by Landau and Khalatnikov. 9 ) **) The bold face letters denote the operators of the Heisenberg picture, at Univ of Iowa-Law Library on June 7, 2015 http://ptp.oxfordjournals.org/ Downloaded from

Because of their unique optical and stimuli-response properties, polydiacetylene-based platforms have been explored as an alternative to complex mechanical and electrical sensing systems. We linked chromic responsive polydiacetylene (PDA) onto a peptide-based molecular recognition element for trinitrotoluene (TNT) molecules in order to provide a system capable of responding to the presence of a TNT target. We first identified the trimer peptide receptor that could induce chromic changes on a PDA backbone. We then investigated the multivalent interactions between TNT and our peptide-based receptor by nuclear magnetic resonance (NMR) spectroscopy. We further characterized various parameters that affected the conjugated PDA system and hence the chromic response, including the size of end-group motifs, the surface density of receptors, and the length of alkane side chains. Taking these necessary design parameters into account, we demonstrated a modular system capable of transducing small-molecule TNT binding into a detectable signal. Our conjugated PDA-based sensor coupled with molecular recognition elements has already proven useful recently in the development of another sensitive and selective electronic sensor, though we expect that our results will also be valuable in the design of colorimetric sensors for small-molecule detection.