Evaluation of table-top lasers for routine infrared ion spectroscopy in the analytical laboratory.

Infrared ion spectroscopy is increasingly recognized as a method to identify mass spectrometry-detected analytes in many (bio)chemical areas and its integration in analytical laboratories is now on the horizon. Commercially available quadrupole ion trap mass spectrometers are attractive ion spectroscopy platforms but operate at relatively high pressures. This promotes collisional deactivation which directly interferes with the multiple-photon excitation process required for ion spectroscopy. To overcome this, infrared lasers having a high instantaneous power are required and therefore a majority of analytical studies have been performed at infrared free electron laser facilities. Proliferation of the technique to routine use in analytical laboratories requires table-top infrared lasers and optical parametric oscillators (OPOs) are the most suitable candidates, offering both relatively high intensities and reasonable spectral tuning ranges. Here, we explore the potential of a range of commercially available high-power OPOs for ion spectroscopy, comparing systems with repetition rates of 10 Hz, 20 kHz, 80 MHz and a continuous-wave (cw) system. We compare the performance for various molecular ions and show that the kHz and MHz repetition-rate systems outperform cw and 10 Hz systems in photodissociation efficiency and offer several advantages in terms of cost-effectiveness and practical implementation in an analytical laboratory not specialized in laser spectroscopy.

Assessment of Disinfection Potential of Q-Switch Nd: YAG Laser on Contaminated Titanium Implant Surfaces.

Peri-implantitis (PI) is a relatively frequent pathology that compromises the overall survival of the dental implant. Adjunctive approaches for the conventional mechanical debridement are being suggested to optimize the treatment of PI. The goal of the study was the assessment of the disinfection potential of the Q-Switch Nd: YAG laser on contaminated titanium implant surfaces. A total of 72 sterile titanium discs were used and divided into three groups: 24 contaminated titanium discs treated with the laser (study Group L), 24 contaminated titanium discs with no treatment (control 1-Group C), and 24 sterile titanium discs with no treatment (control 2-Group S). Multi-species biofilm was used: Porphyromonas gingivalis, Fusobacterium nucleatum, Aggregatibacter actinomycetemcomitans, Streptococcus mutans, Streptococcus sobrinus, and Prevotella intermedia. Commensal bacteria were included also: Actinomyces naeslundii, Actinomyces viscosus, Streptococcus cristatus, Streptococcus gordonii, Streptococcus mitis, Streptococcus oralis, Streptococcus sanguinis, Streptococcus parasanguinis, and Veillonella parvula. Parameters delivered per pulse on the targeted surfaces of the titanium discs were an energy density of 0.597 J/cm2 each pulse, a pulse power of 270 mW, a laser beam spot of 2.4 mm in diameter, and a rate of repetition of 10 Hertz (Hz) for a pulse duration of 6 nanoseconds (ns). The mode was no contact, and a distance of 500 micrometers was used with a total time of irradiation equal to 2 s (s). The collection of microbiological samples was made for all groups; colony-forming units (CFU) were identified by two different practitioners, and the average of their examinations was considered for each sample. The average of the TBC (CFU/mL) was calculated for each group. Values were 0.000 CFU/mL, 4767 CFU/mL, and 0.000 CFU/mL for Group L, Group C, and Group S, respectively. Therefore, the suggested treatment protocol was able to provoke a total disinfection of the contaminated titanium surfaces. A statistical difference was only found between Group L vs. Group C and between Group S vs. Group C. The difference was not significant between Group S and Group L. In conclusion, the present study confirmed that the Q-Switch Nd: YAG laser under our specific conditions can provide a total disinfection of the contaminated titanium surfaces.

Q-Switch Nd:YAG Laser-Assisted Elimination of Multi-Species Biofilm on Titanium Surfaces.

(1) Background: The relatively high prevalence of peri-implantitis (PI) and the lack of a standard method for decontamination of the dental implant surface have pushed us to conduct further research in the field. Bacterial biofilms were found to play a primordial role in the etiology of PI. Therefore, the aim is to evaluate the efficacy of a laser-assisted elimination of biofilm protocol in the removal of a multi-species biofilm on titanium surfaces. (2) Methods: In total, 52 titanium discs (grade 4) were used. The study group consisted of 13 titanium disks contaminated with multi-species biofilms and subsequently irradiated with the laser (T + BF + L). The control groups consisted of the following types of titanium disks: 13 contaminated with multi-species biofilms (T + BF), 13 sterile and irradiated (T + L), 13 sterile and untreated (T). Q-Switch Nd:YAG laser Irradiation parameters were the following: energy density equal to 0.597 J/cm2 per pulse, power equal to 270 milliwatt per pulse, 2.4 mm of spot diameter, and 10 Hz repetition rate for pulse duration of six nanoseconds (ns). The laser irradiation was made during 2 s of total time in non-contact and at 0.5 mm away from the titanium disc surface. After treatment, presence of biofilms on the disks was evaluated by staining with crystal violet (CV), which was measured as optical density at six hundred thirty nm, and statistical analyses were done. (3) Results: the optical density values were 0.004 ± 0.004 for the study group T + BF + L, 0.120 ± 0.039 for group T + BF, 0.006 ± 0.003 for group T + L, and 0.007 ± 0.007 for group T. For the study group, laser treatment resulted in a total elimination of the biofilm, with mean values statistically significantly lower than those of contaminated titanium surfaces and similar to those of sterile titanium surfaces. (4) Conclusions: Our irradiation protocol provided a significant elimination of the multi-species biofilm on titanium surfaces. Laser treated titanium surfaces were biofilm-free, similar to the sterile ones.

Q-Switch Nd:YAG Laser-Assisted Decontamination of Implant Surface.

Peri-implantitis (PI) is an inflammatory disease of peri-implant tissues, it represents the most frequent complication of dental implants. Evidence revealed that microorganisms play the chief role in causing PI. The purpose of our study is to evaluate the cleaning of contaminated dental implant surfaces by means of the Q-switch Nd:YAG (Neodymium-doped Yttrium Aluminum Garnet) laser and an increase in temperature at lased implant surfaces during the cleaning process. Seventy-eight implants (titanium grade 4) were used (Euroteknika, Sallanches, France). Thirty-six sterile implants and forty-two contaminated implants were collected from failed clinical implants for different reasons, independent from the study. Thirty-six contaminated implants were partially irradiated by Q-switch Nd:YAG laser (1064 nm). Six other contaminated implants were used for temperature rise evaluation. All laser irradiations were calibrated by means of a powermetter in order to evaluate the effective delivered energy. The irradiation conditions delivered per pulse on the target were effectively: energy density per pulse of 0.597 J/cm2, pick powers density of 56 mW/cm2, 270 mW per pulse with a spot diameter of 2.4 mm, and with repetition rate of 10 Hz for pulse duration of 6 ns. Irradiation was performed during a total time of 2 s in a non-contact mode at a distance of 0.5 mm from implant surfaces. The parameters were chosen according to the results of a theoretical modeling calculation of the Nd:YAG laser fluency on implant surface. Evaluation of contaminants removal showed that the cleaning of the irradiated implant surfaces was statistically similar to those of sterile implants (p-value ≤ 0.05). SEM analysis confirmed that our parameters did not alter the lased surfaces. The increase in temperature generated at lased implant surfaces during cleaning was below 1 °C. According to our findings, Q-switch Nd:YAG laser with short pulse duration in nanoseconds is able to significantly clean contaminated implant surfaces. Irradiation parameters used in our study can be considered safe for periodontal tissue.

Versatile photoacoustic spectrometer based on a mid-infrared pulsed optical parametric oscillator.

We demonstrate the usefulness of a nanosecond-pulsed single-mode mid-infrared (MIR) optical parametric oscillator (OPO) for photoacoustic (PA) spectroscopic measurements. The maximum wavelength ranges for the signal and idler are 1.4 µm to 1.7 µm and 2.8 µm to 4.6 µm, respectively, with a MIR output power of up to 500 mW, making the OPO useful for different spectroscopic PA trace-gas measurements targeting the major market opportunity of environmental monitoring and breath gas analysis. We perform spectroscopic measurements of methane (CH4), nitrogen dioxide (NO2), and ammonia (NH3) in the 2.8 µm to 3.7 µm wavelength region. The measurements were conducted with a constant flow rate of 300 mL/min, thus demonstrating the suitability of the gas sensor for real-time trace-gas measurements. The acquired spectra are compared with data from the HITRAN database, and good agreement is found, demonstrating a resolution bandwidth of 1.5 cm1. An Allan deviation analysis shows that the detection limit for methane at optimum integration time for the PA sensor is 8 ppbV (nmol/mol) at 105 s of integration time, corresponding to a normalized noise equivalent absorption coefficient of 2.9×10-7 W cm-1 Hz-1/2.

Decontamination of Dental Implant Surfaces by the Er:YAG Laser Beam: A Comparative in Vitro Study of Various Protocols.

Oral rehabilitation with dental implants has revolutionized the field of dentistry and has been proven to be an effective procedure. However, the incidence of peri-implantitis has become an emerging concern. The efficacy of the decontamination of the implant surface, by means of lasers, is still controversial. Previous studies have revealed a reduction in osteoblast adhesion to carbon-contaminated implant surfaces. This in-vitro study aimed to evaluate the decontamination of failed implants by assessing the carbon proportion, after irradiation by low-energy erbium yttrium-aluminum-garnet laser (Er:YAG) (Fotona; 2940 nm, Ljubljana, Slovenia) for a single and for multiple passages, until getting a surface, free of organic matters; to find the appropriate procedure for dental-implant surface-decontamination. Ninety implants were used. Thirty sterile implants were kept as a negative control. Thirty failed implants were irradiated by the Er:YAG laser, for a single passage, and the other thirty, for multiple passages. The parameters used in our experiments were an irradiation energy of 50 mJ, frequency of 30 Hz, and an energy density of 3.76 J/cm². A sapphire tip, with a length of 8 mm, was used with concomitant water spray irrigation, under air 6 and water spray 4. Super short pulse mode (SSP) was of 50 µs; irradiation speed being 2 mm/s. We used energy-dispersive X-ray spectroscopy (EDX) to evaluate the carbon proportion on the surfaces of the sterile implants, the contaminated, and the lased implants, with one (LX1) and with three passages (LX3). Statistical analysis was performed by ANOVA. Results showed mean difference between the three groups (contaminated, LX1, and LX3) with p < 0.0001, as between LX1 and Group A (p < 0.0001), while the difference between LX3 and the control group was not statistically significant. The decontamination of the implant surfaces with a low-energy Er:YAG laser with three passages, appeared to be an encouraging approach.

Off-axis quartz-enhanced photoacoustic spectroscopy using a pulsed nanosecond mid-infrared optical parametric oscillator: publisher's note.

This publisher's note corrects an affiliation error in Opt. Lett.41, 4118 (2016)OPLEDP0146-959210.1364/OL.41.004118.

Doubling the far-field resolution in mid-infrared microscopy.

The spatial resolution in far-field mid-infrared (λ>2.5 µm) microscopy and micro-spectroscopy remains limited with the full-width at half maximum of the point-spread function ca. λ/1.3; a value that is very poor in comparison to that commonly accessible with visible and near-infrared optics. Hereafter, it is demonstrated however that polymer beads that are centre-to-centre spaced by λ/2.6 can be resolved in the mid-infrared. The more than 2-fold improvement in resolution in the far-field is achieved by exploiting a newly constructed scanning microscope built around a mid-infrared optical parametric oscillator and a central solid-immersion lens, and by enforcing the linear polarization unidirectional resolution enhancement with a novel and robust specimen error minimization based on a particle swarm optimization. The method is demonstrated with specimens immersed in air and in water, and its robustness shown by the analysis of dense and complex self-assembled bead islands.

Off-axis quartz-enhanced photoacoustic spectroscopy using a pulsed nanosecond mid-infrared optical parametric oscillator.

A trace-gas sensor, based on quartz-enhanced photoacoustic spectroscopy (QEPAS), consisting of two acoustically coupled micro-resonators (mR) with an off-axis 20 kHz quartz tuning fork (QTF) is demonstrated. The complete acoustically coupled mR system is optimized based on finite-element simulations and is experimentally verified. The QEPAS sensor is pumped resonantly by a nanosecond pulsed single-mode mid-infrared optical parametric oscillator. The sensor is used for spectroscopic measurements on methane in the 3.1-3.5 µm wavelength region with a resolution bandwidth of 1 cm-1 and a detection limit of 0.8 ppm. An Allan deviation analysis shows that the detection limit at the optimum integration time for the QEPAS sensor is 32 ppbv at 190 s, and that the background noise is due solely to the thermal noise of the QTF.

Treatment of dentinal hypersensitivity by means of Nd:YAP Laser: a preliminary in vitro study.

OBJECTIVE: The aim of this study is to evaluate the effectiveness of Nd:YAP laser to seal dentinal tubules at different parameters. MATERIAL AND METHODS: 24 caries-free human wisdom impacted molars were used. The crowns were sectioned transversally in order to totally expose the dentin. The smear layer was removed by a 1 min application of EDTA. Each surface was divided into four quadrants, but only three quadrants were irradiated at a different output power setting (irradiation speed: 1 mm/sec; optical fiber diameter: 320 µm; tangential incidence of beam and in noncontact mode). Samples were smeared with a graphite paste prior to laser irradiation. All specimens were sent for SEM analysis. Pulp temperature increases in additional twenty teeth were measured by a thermocouple. RESULTS: Morphological changes in dentin surfaces depend on the value of used energy density. Higher energy densities (2 W-4 W; 200-400 mJ; pulse duration: 100 m sec.; and 10 Hz) induce higher dentin modifications. Our results confirmed that Nd:YAP laser irradiations can lead to total or partial occlusion of dentin tubules without provoking fissures or cracks. Measurements of pulp temperature increases showed that Nd:YAP laser beam can be considered as harmless for pulp vitality for following irradiation conditions: 2 W (200 mJ) to 4 W (400 mJ) with an irradiation speed of 1 mm/sec; fiber diameter: 320 micrometers; 10 Hz; pulse duration: 100 m sec; noncontact mode and in tangential incidence to exposed dentin. The perpendicular incidence of the laser beam on exposed dentin may injure pulp vitality even at low output power of 3 W. CONCLUSIONS: Nd:YAP laser beam was able to seal the dentin tubules without damaging dentinal surfaces and without harming pulp vitality. Nd:YAP laser is effective and may be safely used for future in vivo treatments of dentinal hypersensitivity under certain conditions.

Gingiva laser welding: preliminary study on an ex vivo porcine model.

OBJECTIVE: The use of lasers to fuse different tissues has been studied for 50 years. As none of these experiments concerned the oral soft tissues, our objective was to assess the feasibility of laser gingiva welding. MATERIALS AND METHODS: Porcine full-thickness gingival flaps served to prepare calibrated samples in the middle of which a 2 cm long incision was closed, either by conventional suture or by laser tissue welding (LTW). To determine the irradiation conditions yielding the best tensile strength, 13 output power values, from 0.5 to 5 W, delivered either at 10 Hz or in continuous wave mode, were tested on six indocyanine green (ICG) concentrations, from 8% to 13% (588 samples). Then, some samples served to compare the tensile strength between the laser welded and the sutured gingiva; the other samples were histologically processed in order to evaluate the thermal damage extent. The temperature rise during the LTW was measured by thermocouples. Another group of 12 samples was used to measure the temperature elevation by thermal camera. RESULTS: In the laser welding groups, the best tensile strength (p<0.05) was yielded by the 9% ICG saline solution (117 mM) at 4.5 W, 10 Hz, and a fluence of 31.3 kJ/cm(2). The apposition strength revealed no statistically significant difference (p<0.05) between the sutured and the laser welded gingiva at 4.5 W, 10 Hz, and 9% ICG solution. The mean temperature was 74±5.4°C at the upper surface and 42±8.9°C at the lower surface. The damaged zone averaged 333 µm at the upper surface. CONCLUSIONS: The 808 nm diode laser associated with ICG can achieve oral mucosa LTW, which is conceivable as a promising technique of gingival repair.

High resolution imaging with differential infrared absorption micro-spectroscopy.

Although confocal infrared (IR) absorption micro-spectroscopy is well established for far-field chemical imaging, its scope remains restricted since diffraction limits the spatial resolution to values a little above half the radiation wavelength. Yet, the successful implementations of below-the-diffraction limit far-field fluorescence microscopies using saturated irradiation patterns for example for stimulated-emission depletion and saturated structured-illumination suggest the possibility of using a similar optical patterning strategy for infrared absorption mapping at high resolution. Simulations are used to show that the simple mapping of the difference in transmitted/reflected IR energy between a saturated vortex-shaped beam and a Gaussian reference with a confocal microscope affords the generation of high-resolution vibrational absorption images. On the basis of experimentally relevant parameters, the simulations of the differential absorption scheme reveal a spatial resolution better than a tenth of the wavelength for incident energies about a decade above the saturation threshold. The saturated structured illumination concepts are thus expected to be compatible with the establishment of point-like point-spread functions for measuring the absorbance of samples with a scanning confocal microscope recording the differential transmission/reflection.

Vibrational sum-frequency generation activity of a 2,4-dinitrophenyl phospholipid hybrid bilayer: retrieving orientational parameters from a DFT analysis of experimental data.

The vibrational nonlinear activity of films of 2,4-dinitrophenyl phospholipid (DNP) at the solid interface is measured by sum-frequency generation spectroscopy (SFG). Hybrid bilayers are formed by a Langmuir-Schaefer approach in which the lipid layer is physisorbed on top of a self-assembled monolayer of dodecanethiol on Pt with the polar heads pointing out from the surface. The SFG response is investigated in two vibrational frequency domains, namely, 3050-2750 and 1375-1240 cm(-1). The first region probes the CH stretching modes of DNP films, and the latter explores the vibrational nonlinear activity of the 2,4-dinitroaniline moiety of the polar head of the lipid. Analysis of the CH stretching vibrations suggests substantial conformational order of the aliphatic chains with only a few gauche defects. To reliably assign the detected SFG signals to specific molecular vibrations, DFT calculations of the IR and Raman activities of molecular models are performed and compared to experimental solid-state spectra. This allows unambiguous assignment of the observed SFG vibrations to molecular modes localized on the 2,4-dinitroaniline moiety of the polar head of DNP. Then, SFG spectra of DNP in the 1375-1240 cm(-1) frequency range are simulated and compared with experimental ones, and thus the 1,4-axis of the 2,4-dinitrophenyl head is estimated to have tilt and rotation angles of 45±5° and 0±30°, respectively.

A framework for far-field infrared absorption microscopy beyond the diffraction limit.

A framework is proposed for infrared (IR) absorption microscopy in the far-field with a spatial resolution below the diffraction limit. The sub-diffraction resolution is achieved by pumping a transient contrast in the population of a selected vibrational mode with IR pulses that exhibit alternating central minima and maxima, and by probing the corresponding absorbance at the same wavelength with adequately delayed Gaussian pulses. Simulations have been carried out on the basis of empirical parameters emulating patterned thin films of octadecyltrichlorosilane and a resolution of 250 nm was found when probing the CH2 stretches at 3.5 µm with pump energies less than ten times the vibrational saturation threshold.

Structures of bare and hydrated [Pb(aminoacid-H)]+ complexes using infrared multiple photon dissociation spectroscopy.

Infrared multiple-photon dissociation (IRMPD) spectroscopy was used to determine the gas-phase structures of deprotonated Pb(2+)/amino acid (Aa) complexes with and without a solvent molecule present. Five amino acid complexes with side chains containing only carbon and hydrogen (Ala, Val, Leu, Ile, Pro) and one with a basic side chain (Lys) were compared. These experiments demonstrated that all [Pb(Aa-H)](+) complexes have Pb(2+) covalently bound between the amine nitrogen and carbonyl oxygen. The nonhydrated complexes containing Ala, Val, Leu, Ile, and Pro are amine-deprotonated, whereas the one containing Lys is deprotonated at its carboxylic acid. The difference is attributed to the polar and basic side chain of lysine, which helps stabilize Pb(2+). IRMPD spectroscopy was also performed on the monohydrated analogues of the [Pb(Aa-H)](+) complexes. The [Pb(Aa-H)H(2)O](+) complexes, where Aa = Ala, Val, Leu, and Ile, exhibited two N-H stretches as well as a carboxylic acid O-H and a PbO-H stretch. Hence, their structures are monohydrated versions of the amine-deprotonated [Pb(Aa-H)](+) complexes where a proton transfer has occurred from the lead-bound water to the deprotonated amine. The IRMPD spectrum and calculations suggest that [Pb(Pro-H)H(2)O](+) has a hydrated carboxylate salt structure. The structure of [Pb(Lys-H)H(2)O](+) was also carboxyl-deprotonated, but Pb(2+) is bound to the carbonyl oxygen and the amine nitrogen, with one of the protons belonging to the water transferred to the basic side chain. This results in an intramolecular hydrogen bond that does not absorb in the region of the spectrum probed in these experiments. The IRMPD spectra and structural characterizations were confirmed and aided by infrared spectra calculated at the B3LYP/6-31+G(d,p) level of theory and 298 K enthalpies and Gibbs energies using the MP2(full)/6-311++G(2d,2p) method on the B3LYP geometries.

Orientational analysis of dodecanethiol and p-nitrothiophenol SAMs on metals with polarisation-dependent SFG spectroscopy.

Polarisation-dependent sum frequency generation (SFG) spectroscopy is used to investigate the orientation of molecules on metallic surfaces. In particular, self-assembled monolayers (SAMs) of dodecanethiol (DDT) and of p-nitrothiophenol (p-NTP), grown on Pt and on Au, have been chosen as models to highlight the ability of combining ppp and ssp polarisations sets (representing the polarisation of the involved beams in the conventional order of SFG, Vis and IR beam) to infer orientational information at metallic interfaces. Indeed, using only the ppp set of data, as it is usually done for metallic surfaces, is not sufficient to determine the full molecular orientation. We show here that simply combining ppp and ssp polarisations enables both the tilt and rotation angles of methyl groups in DDT SAMs to be determined. Moreover, for p-NTP, while the SFG active vibrations detected with the ppp polarisation alone provide no orientational information, however, the combination with ssp spectra enables to retrieve the tilt angle of the p-NTP 1,4 axis. Though orientational information obtained by polarisation-dependent measurements has been extensively used at insulating interfaces, we report here their first application to metallic surfaces.

Noncritical singly resonant synchronously pumped OPO for generation of picosecond pulses in the mid-infrared near 6.4 microm.

The recently developed chalcopyrite CdSiP(2) is employed in a picosecond, 90 degrees -phase-matched, synchronously pumped, optical parametric oscillator pumped at 1064 nm to produce steady-state idler pulses near 6.4 microm with an energy as high as 2.8 microJ at 100 MHz, in a train of 2-micros-long macropulses following at a repetition rate of 25 Hz. Without an intracavity etalon, the 12.6-ps-long micropulses have a spectral width of 240 GHz.

Theoretical simulation of vibrational sum-frequency generation spectra from density functional theory: application to p-nitrothiophenol and 2,4-dinitroaniline.

The molecular orientation of adsorbed molecules forming self-assembled monolayers can be determined by combining vibrational sum-frequency generation (SFG) measurements with quantum chemical calculations. Herein, we present a theoretical methodology used to simulate the SFG spectra for different combinations of polarizations. These simulations are based on calculations of the IR vectors and Raman tensors, which are obtained from density functional theory computations. The dependency of the SFG vibrational signature with respect to the molecular orientation is presented for the molecules p-nitrothiophenol and 2,4-dinitroaniline. It is found that a suitable choice of basis set as well as of exchange-correlation (XC) functional is mandatory to correctly simulate the SFG intensities and consequently provide an accurate estimation of the adsorbed molecule orientation. Comparison with experimental data shows that calculations performed at the B3LYP/6-311++G(d,p) level of approximation provide good agreement with experimental frequencies, and with IR and Raman intensities. In particular, it is demonstrated that polarization and diffuse functions are compulsory for reproducing the IR and Raman spectra, and consequently vibrational SFG spectra, of systems such as p-nitrothiophenol. Moreover, the investigated XC functionals reveal their influence on the relative intensities, which show rather systematic variations with the amount of Hartree-Fock exchange. Finally, further aspects of the modeling are revealed by considering the frequency dependence of the Raman tensors.

Adsorption properties of the penicillin derivative DTPA on gold substrates.

Despite the large number of articles and patents dealing with penicillin and other beta-lactam antibiotics, there have been no reports about the self-assembly of such substances as monolayers on gold surfaces. The main reason stems from the high reactivity of the beta-lactam ring, which hinders the development of molecules possessing this entity together with a metal-anchoring function. Herein, we present the synthesis of a novel molecule, 6-[(R,S)-5-(1,2-dithiolan-3-yl)pentanoyl-amino]-penicillanic acid, which combines the beta-lactam ring and a metal-anchoring group. Using spectroscopic tools, we demonstrate the chemisorption of this compound on gold as self-assembled monolayers without any alteration of the penicillin pharmacophore and document its reactivity towards a penicillin-binding protein, BlaR-CTD. Our work is a preliminary step towards the development of new biosensors and well-ordered protein arrays, both based on the high affinity of penicillin for penicillin-binding proteins.

Sum-frequency generation spectroscopy of DNA monolayers.

The anchoring of thiolated single-stranded DNA (HS-ssDNA) monolayers onto platinum substrates was investigated by sum-frequency generation spectroscopy. Different buffer solutions were used for the preparation of the adlayers. Vibrational fingerprints in the 2700-3100 cm(-1) spectral range showed the intercalation of Tris/EDTA (TE) buffer molecules within the HS-ssDNA self-assembled monolayer. Buffer contribution to SFG can be quenched either by using SFG inactive molecules like KH(2)PO(4)/K(2)HPO(4)/NaCl (PBS) or by repeated rinsing of the DNA layer with pure water. Comparing the SFG spectra of HS-ssDNA and mercaptohexanol (MCH), which had been self-assembled onto the same substrate, enabled us to infer ordering of the anchor arms and strong disordering of the DNA strands of HS-ssDNA monolayers self-assembled on platinum.