Ryszard Jankowiak

Electrochemically deposited metal nanoparticles for enhancing the performance of microfluidic MEMS in biochemical analysis

The fabrication and evaluation of the analytical performance of integrated microfluidic MEMS modified with electrochemically deposited metal nanoparticles are described in this paper. The microfluidic MEMS is a hydride system that comprise two layers, poly-dimethylsiloxane (PDMS) and glass, which in turn enclose a micro channels network and a set of 15 micro electrodes, respectively. The mechanism of electrokinetic phenomenon and electrochemical detection were applied for performing injection and separation, and sensing the components of a biochemical mixture, respectively. The technique of electrochemical deposition was employed for depositing nanoparticles of gold, palladium and platinum on the surface of integrated microelectrodes. The nanoparticles-modified micro electrodes were characterised electrochemically and using scanning electron microscope (SEM). Importantly, the nanoparticles-based decoupler has significantly enhanced the analytical performance of the microfluidic MEMS, where detection limits in the low nanomolar range were recorded for the targeted analytes.

Site Selective and Single Complex Laser-Based Spectroscopies: A Window on Excited State Electronic Structure, Excitation Energy Transfer, and Electron–Phonon Coupling of Selected Photosynthetic Complexes

Site Selective and Single Complex Laser-Based Spectroscopies: A Window on Excited State Electronic Structure, Excitation Energy Transfer, and Electron Phonon Coupling of Selected Photosynthetic Complexes Ryszard Jankowiak,* Mike Reppert, Valter Zazubovich, J€org Pieper, and Tonu Reinot Department of Chemistry, Kansas State University, Manhattan, Kansas 66506, United States Department of Physics, Concordia University, Montreal H4B1R6 Quebec, Canada Max-Volmer-Laboratories for Biophysical Chemistry, Technical University of Berlin, Germany Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia

On the Shape of the Phonon Spectral Density in Photosynthetic Complexes

We provide a critical assessment of typical phonon spectral densities, J(ω), used to describe linear and nonlinear optical spectra in photosynthetic complexes. Evaluation is based on a more careful comparison to experiment than has been provided in the past. J(ω) describes the frequency-dependent coupling of the system to the bath and is an important component in calculations of excitation energy transfer times. On the basis of the shape of experimental J(ω) obtained for several photosynthetic complexes, we argue that the shape of J(ω) strongly depends on the pigment-protein complex. We show that many densities (especially the Drude-Lorentz/constant damping Brownian oscillator) display qualitatively wrong behavior when compared to experiment. Because of divergence of J(ω) at zero frequency, the Brownian oscillator cannot fit a single-site spectrum correctly. It is proposed that a log-normal distribution can be used to fit experimental data and exhibits desired attributes for a physically meaningful phonon J(ω), in contrast to several commonly used spectral densities which exhibit low-frequency behavior in qualitative disagreement with experiment. We anticipate that the log-normal J(ω) function proposed in this work will be further tested in theoretical modeling of both time- and frequency-domain data.

Dispersive kinetic processes, optical linewidths and dephasing in amorphous solids

Abstract A theory which describes the dispersive behavior associated with (i) nonphotochemical hole growth (or photochemical hole growth with a distribution of photoproduct states) and (ii) spontaneous hole filling is developed and applied to existing experimental data. For certain systems, the hole growth data demand that hole filling during the burn (HFDB) be considered. The relationship of this filling to the recently discovered phenomenon of laser-induced hole filling (LIHF) is discussed. The above theory is based on the TLS model, with both intrinsic and extrinsic TLS (TLS int , TLS ext ) taken into account. The TLS ext represent the subset of bistable configurations which interact strongly with or are created by the impurity. The two types of TLS are characterized by markedly different distribution function parameters. Finally, the question of whether holewidths can be used to provide the optical dephasing time is addressed. A mechanism for spectral diffusion (broadening) of holes due to slow (>T 1 ) TLS relaxation processes is proposed. Conditions under which the temperature power laws for optical dephasing and “slow” spectral diffusion may be the same are defined.

Novel biosensor chip for simultaneous detection of DNA-carcinogen adducts with low-temperature fluorescence.

A monoclonal antibody (MAb)-gold biosensor chip with low-temperature laser-induced fluorescence detection for analysis of DNA-carcinogen adducts is described. Optimization of the detection limit, dynamic range, and biosensing applicability of the MAb-gold biosensor chip was achieved by: (1) using dithiobis(succinimidyl propionate (DSP)) as a protein linker and (2) employing recombinant protein A to provide oriented immobilization of the MAbs. The use of DSP, which has a short methylene chain length, led to faster protein binding kinetics and higher protein surface density than a longer dithiobis(succinimidyl undecanoate) (DSU) linker. The incorporation of recombinant protein A increased the distance between the oriented MAb-bound analytes and the gold surface. The increased distance minimized fluorescence quenching, resulting in about a 10-fold increase in the fluorescence signal in comparison with a chip without protein A. The improved chip architecture was used to demonstrate that biosensing of two structurally similar benzo[a]pyrene (BP)-derived DNA adducts, BP-6-N7Gua and BP-diolepoxide-10-N2dG, bound to two specific MAbs immobilized from a mixture at the same address on the chip, is feasible. These mutagenic adducts are formed by one-electron oxidation and monooxygenation pathways, and are depurinating and stable DNA adducts, respectively. It is shown that the DNA adducts can be easily identified at the same address using time-resolved, low-temperature laser-based fluorescence spectroscopy. The current limit of detection is in the low femtomole range. These results indicate that a single biosensor chip consisting of a Au/DSP/protein A/MAb nano-assembly, with analyte-specific MAbs and low-temperature fluorescence detection should be suitable for simultaneous detection and quantitation of the above adducts, as well as the luminescent antigens for which selective MAbs exist.

Dispersive kinetics of nonphotochemical hole growth for oxazine 720 in glycerol, polyvinyl alcohol and their deuterated analogues

Abstract Dispersive hole growth kinetic data obtained with burn intensities in the nW to μW/cm 2 range are reported for the laser dye oxazine 720 in glycerol glasses and polyvinyl alcohol polymer films. The data are well described by a theory that employs a distribution function for the hole burning rate constant derived from a Gaussian distribution for the tunnel parameter of extrinsic two-level systems. The linear electron-phonon coupling is taken into account in the analysis. An approach for calculating the nonphotochemical hole burning quantum yield as a function of the hole depth is described. Deuteration of the hydroxyl proton of the amorphous hosts reduces the average hole burning quantum yield by a factor of ≈ 20, indicating that large amplitude motion of this proton is an important component of the tunneling coordinate. Temperature-dependent data are used to prove that the dispersive hole burning kinetics are independent of temperature between 1.6 and 7 K (the range studied).

Effects of detergent on the excited state structure and relaxation dynamics of the photosystem II reaction center: A high resolution hole burning study.

Low temperature (4.2 K) absorption and hole burned spectra are reported for a stabilized preparation (no excess detergent) of the photosystem II reaction center complex. The complex was studied in glasses to which detergent had and had not been added. Triton X-100 (but not dodecyl maltoside) detergent was found to significantly affect the absorption and persistent hole spectra and to disrupt energy transfer from the accessory chlorophyll a to the active pheophytin a. However, Triton X-100 does not significantly affect the transient hole spectrum and lifetime (1.9 ps at 4.2 K) of the primary donor state, P680*. Data are presented which indicate that the disruptive effects of Triton X-100 are not due to extraction of pigments from the reaction center, leaving structural perturbations as the most plausible explanation. In the absence of detergent the high resolution persistent hole spectra yield an energy transfer decay time for the accessory Chl a QY-state at 1.6 K of 12 ps, which is about three orders of magnitude longer than the corresponding time for the bacterial RC. In the presence of Triton X-100 the Chl a QY-state decay time is increased by at least a factor of 50.

Insight into the electronic structure of the CP47 antenna protein complex of photosystem II: hole burning and fluorescence study.

We report low temperature (T) optical spectra of the isolated CP47 antenna complex from Photosystem II (PSII) with a low-T fluorescence emission maximum near 695 nm and not, as previously reported, at 690-693 nm. The latter emission is suggested to result from three distinct bands: a lowest-state emission band near 695 nm (labeled F1) originating from the lowest-energy excitonic state A1 of intact complexes (located near 693 nm and characterized by very weak oscillator strength) as well as emission peaks near 691 nm (FT1) and 685 nm (FT2) originating from subpopulations of partly destabilized complexes. The observation of the F1 emission is in excellent agreement with the 695 nm emission observed in intact PSII cores and thylakoid membranes. We argue that the band near 684 nm previously observed in singlet-minus-triplet spectra originates from a subpopulation of partially destabilized complexes with lowest-energy traps located near 684 nm in absorption (referred to as AT2) giving rise to FT2 emission. It is demonstrated that varying contributions from the F1, FT1, and FT2 emission bands led to different maxima of fluorescence spectra reported in the literature. The fluorescence spectra are consistent with the zero-phonon hole action spectra obtained in absorption mode, the profiles of the nonresonantly burned holes as a function of fluence, as well as the fluorescence line-narrowed spectra obtained for the Q(y) band. The lowest Q(y) state in absorption band (A1) is characterized by an electron-phonon coupling with the Huang-Rhys factor S of approximately 1 and an inhomogeneous width of approximately 180 cm(-1). The mean phonon frequency of the A1 band is 20 cm(-1). In contrast to previous observations, intact isolated CP47 reveals negligible contribution from the triplet-bottleneck hole, i.e., the AT2 trap. It has been shown that Chls in intact CP47 are connected via efficient excitation energy transfer to the A1 trap near 693 nm and that the position of the fluorescence maximum depends on the burn fluence. That is, the 695 nm fluorescence maximum shifts blue with increasing fluence, in agreement with nonresonant hole burned spectra. The above findings provide important constraints and parameters for future excitonic calculations, which in turn should offer new insight into the excitonic structure and composition of low-energy absorption traps.

Structured hole burned spectra of the primary donor state absorption region of Rhodopseudomonas viridis

Abstract Structured hole burned spectra for P960 of Rps. viridis are reported which, for appropriate burn wavelengths, exhibit four holes (including a zero-phonon hole). Burn wavelength-dependent spectra and other factors indicate that the hole structure is not contributed to by reaction center heterogeneity or impurity. The data are consistent with there being two adiabatic states, |Z>* and |X>*, which contribute significantly to the P960 absorption profile, with |X>* defined as the lower energy state (by ≈300 cm −1 ). The zero-phonon hole can be assigned as a feature belonging to the hole associated with |X>* and possesses a width of 10 cm −1 at 4.2 K. This width yields a decay time of 1 ps for |X>* and, consequently, a connection with time domain studies of the primary electron donor state. A number of models for the existence of the two absorbing states are considered. The following two models for |X>* and |Z>* appear to be plausible: that they are admixtures of the neutral exciton state and an intra-dimer charge transfer state of the special pair (P) or they are admixtures of P* and a charge transfer state between P and the bacteriochlorophyll monomer on the active side.

Challenges facing an understanding of the nature of low-energy excited states in photosynthesis

While the majority of the photochemical states and pathways related to the biological capture of solar energy are now well understood and provide paradigms for artificial device design, additional low-energy states have been discovered in many systems with obscure origins and significance. However, as low-energy states are naively expected to be critical to function, these observations pose important challenges. A review of known properties of low energy states covering eight photochemical systems, and options for their interpretation, are presented. A concerted experimental and theoretical research strategy is suggested and outlined, this being aimed at providing a fully comprehensive understanding.