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The intriguing network of antibody–antigen (Ab–Ag) interactions is highly governed by environmental perturbations and the nature of biomolecular interaction. Protein–protein interactions (PPIs) have potential applications in developing protein-adsorption-based sensors and nano-scale materials. Therefore, characterizing PPIs in the presence of a nanomaterial at the molecular level becomes imperative. The present work involves the investigation of antiferritin–ferritin (Ab–Ag) protein interactions under the influence of tungsten disulfide quantum dots (WS2 QDs). Isothermal calorimetry and contact angle measurements validated the strong influence of WS2 QDs on Ab–Ag interactions. The interfacial signatures of nano–bio-interactions were evaluated using sum frequency generation vibration spectroscopy (SFG-VS) at the air–water interface. Our SFG results reveal a variation in the tilt angle of methyl groups by ∼12° ± 2° for the Ab–Ag system in the presence of WS2 QDs. The results illustrated an enhanced ordering of water molecules in the presence of QDs, which underpins the active role of interfacial water molecules during nano–bio-interactions. We have also witnessed a differential impact of QDs on Ab–Ag by raising the concentration of the Ab–Ag combination, which showcased an increased inter-molecular interaction among the Ab and Ag molecules and a minimal influence on the methyl tilt angle. These findings suggest the formation of stronger and ordered Ab–Ag complexes upon introducing WS2 QDs in the aqueous medium and signify the potentiality of WS2 QDs relevant to protein-based sensing assays. [ABSTRACT FROM AUTHOR]

Jet velocity and jet power are the crucial parameters that govern the release profile of drugs/vaccines in needle-free injection systems, where salts are considered as one of the essential constituents of drugs/vaccines as adjuvants. However, the impact of salts on the generation of laser-induced liquid microjets that have shown tremendous potential for drug delivery has remained unexplored. Here, we have investigated the influence of Hofmeister ions on the velocity of laser-induced liquid jets in rhodamine 6G (Rh6G) dye solution. A comprehensive experimental approach is adopted to find out the values of the liquid microjet velocity by varying the parameters, such as input energy of the laser beam, concentrations of the dye, and specific Hofmeister ions in the aqueous solution. From our experimental findings, it is observed that the presence of ions significantly influences the jet velocity that follows the Hofmeister series: SO 4 2 − > I − > SCN − . This, in turn, governs the ion-specific penetration depth of liquid jets as simulated for the model soft tissues. The observed Hofmeister trend in the jet velocity values showcases the possible specific-ion interactions between anions and Rh6G molecules in the aqueous solution. Our detailed experimental findings on ion-specific jet velocity and jet power could be beneficial in designing needle-free drug delivery systems with controlled penetration depths. [ABSTRACT FROM AUTHOR]

Advancement in molecularly imprinted biomimetics has aided in developing robust artificial recognition-based materials, which can be customized for bio/chemo-sensing of distinct molecules. The present study reports a simple one-step synthesis and analysis of protein-imprinted polymer thin films as a recognition element directly onto a solid support. Dopamine has been explored as a versatile functional monomer for a molecularly imprinted polymer (MIP) matrix to fabricate polydopamine (PDA) thin films with bovine hemoglobin as a template protein molecule. A detailed molecular-level insight into the recognition of the template molecule at each step has been investigated using vibrational sum frequency generation (VSFG) spectroscopy. A suitable PDA-coated thin film is selected based on the extent of polymerized intermediates formed after non-imprinted polymer fabrication at different time durations. An optimally prepared film of MIP is specified by observing the spectral signature of the methyl groups from protein molecules at the air–polymer interface. The template removal from MIP films after the washing procedure and subsequent re-binding of the protein molecules were evaluated by VSFG spectroscopy. The insightful molecular-level findings from SFG spectroscopy demonstrate the fabrication of an imprinted matrix as a label-free chemical sensor. [ABSTRACT FROM AUTHOR]

Attenuated total reflectance Fourier transform infrared spectroscopy and sum frequency generation (SFG) vibrational spectroscopy have been employed to probe the molecular structure of N,N-dimethylformamide (DMF) and water mixture by varying the concentration of DMF. From the bulk studies, we observed a gradual decrease in the intensity with a continuous blue shift in the OH-stretch region with the increase in the DMF concentration. In contrast, no significant blue shift in the OH-stretch region is noticed from the SFG spectra collected from the air–aqueous binary mixture interface as a function of DMF concentration. However, the impact of DMF is found to be disruptive in nature toward the existing hydrogen bonding network of the pristine water at the interfacial region. Interestingly, in the CH-stretch region, the vibrational signatures of the DMF molecule show blue shifts, as proposed in earlier studies. We have calculated the molecular tilt angle of the methyl group of the DMF molecule as a function of DMF concentration. For the case of neat DMF, the observed tilt angle is ∼17.7° with respect to the surface normal. The value of tilt angle decreases with the decrease in DMF concentration and reaches a value of ∼1.7° for a mole fraction of 0.5, and it further increases with the decrease in DMF concentration. It achieves a value of ∼20° for the dilute DMF mole fraction of 0.05 in the binary mixture. This indicates that DMF molecules at the air–binary mixture interface are placing their methyl groups more toward the normal for the intermediate DMF concentrations. [ABSTRACT FROM AUTHOR]

The use of a liquid microjet as a possible source of interest for Second Harmonic Generation (SHG) and Sum Frequency Generation (SFG) spectroscopy is examined. We measured non-resonant SHG scattering patterns from the air/water interface of a microjet of pure water and observe a strong enhancement of the SHG signal for certain scattering angles. These enhancements can be explained by the optical properties and the shape of the liquid microjet. SFG experiments at the surface of a liquid microjet of ethanol in air show that it is also possible to measure the coherent vibrational SFG spectrum of the ethanol/air interface in this way. Our findings are useful for future far-UV or X-ray based nonlinear optical surface experiments on liquid jets. In addition, combined X-ray photoelectron spectroscopy and SHG/SFG measurements are feasible, which will be very useful in improving our understanding of the molecular foundations of electrostatic and chemical surface properties and phenomena. [ABSTRACT FROM AUTHOR]

The optimum experimental geometry for visible-infrared sum-frequency generation experiments depends rather sensitively on the molecules adsorbed at the surface, their orientation, and the nature of the adjacent bulk media. We consider the commonly encountered case of methyl groups situated at air-water, air-gold, and polymer-water interfaces. We provide expressions that may be used to determine the optimal visible and IR beam incident angles, considering the symmetric and antisymmetric modes separately and then together. The analysis is carried out for co-propagating (collinear and non-collinear geometries) and counter-propagating configurations. We first consider that one or more vibrational modes are of interest, and the goal is to study them quantitatively under a single polarization scheme; our results enable the user to set the beam angles for such an experiment. In the second case, molecular orientation information is desired, and so the calibrated response is required in all accessible polarization schemes for full characterization of the nonlinear susceptibility tensor. [ABSTRACT FROM AUTHOR]

A detailed model is presented that describes the temporal and spectral interference patterns resulting from phase-recovery infrared-visible sum-frequency spectroscopy. Included in this model are the effects of dispersive elements other than the phase shifting unit placed between the sample and local oscillator signals. This inclusion is critical when considering the interference patterns arising from studies of buried interfaces. Furthermore, in the midinfrared where it is difficult to have high visibility of the fringes, it is demonstrated that local field corrections have a significant effect on the shape of the interference pattern. By collecting and subsequently fitting a two-dimensional interference pattern displaying both temporal and spectral fringes, a complete characterization of all these effects is possible. [ABSTRACT FROM AUTHOR]

We demonstrate that the thickness of a polymer film may be determined by a simple analysis of the interference fringes observed in a transparent region of its transmission spectrum. By measuring the transmission spectrum of the uncoated substrate in the same wavelength region, we can determine the dispersion of the refractive index for the substrate and film and the thickness of the film, without prior knowledge of the optical constants of any of the materials. The results of our approach agree with measurements obtained by a direct contact method. This analysis provides a fast, simple, and nondestructive method of thickness measurement using equipment available in many teaching laboratories. The method enables students to make routine thickness measurements while introducing them to refractive index dispersion, Fresnel coefficients, thin film interference, and regression analysis. [ABSTRACT FROM AUTHOR]