Martín G. González

Bio: Martín G. González is an academic researcher from University of Buenos Aires. The author has contributed to research in topics: Photoacoustic effect & Laser. The author has an hindex of 11, co-authored 44 publications receiving 354 citations. Previous affiliations of Martín G. González include Technische Universität München & National Scientific and Technical Research Council.

Determination of the absolute fluorescence quantum yield of rhodamine 6G with optical and photoacoustic methods--providing the basis for fluorescence quantum yield standards.

Abstract: To establish the methodical basis for the development and certification of fluorescence quantum yield standards, we determined the fluorescence quantum yield Φf of rhodamine 6G (R6G) with two absolute methods with complementary measurement principles, here optical spectroscopy using an integrating sphere setup and pulsed laser photoacoustic spectroscopy (PAS). For the assessment of aggregation- and reabsorption-induced distortions of measured fluorescence quantum yields and procedures for the reliable consideration of such effects, this systematic comparison was performed in ethanol and in water employing different concentrations of R6G. In addition, the relative and absolute fluorescence quantum yields of these solutions were obtained with a calibrated spectrofluorometer and a commercialized integrating sphere setup. Based upon this systematic comparison, experimental advantages and systematic sources of variation were identified for both methods.

Strong size-dependent photoacoustic effect on gold nanoparticles by laser-induced nanobubbles

Abstract: In this paper we propose a mathematical model and an approximate equation to explain the behavior found on the photoacoustic effect generated by laser-induced nanobubbles in colloidal gold solutions. To obtain the equation, we developed a simulation program based on the widely known Rayleigh–Plesset model. A set of measurements was carried out to assess its accuracy on real samples. The equation gives a good approximation for spherical gold nanoparticles with sizes between 10 and 80 nm, and laser fluences larger than the fluence threshold for bubble formation.

Differential, LED-excited, resonant NO2 photoacoustic system

Abstract: We introduce the application of a differential microphone in an LED-excited photoacoustic system devoted to NO2 measurement. The microphone ports pick up out-of-phase signals generated in two resonators, thus achieving a larger electrical signal and good common mode noise rejection. The reduced noise floor and LEDs with higher optical power, made it possible to measure NO2 down to 60 ppbV, a figure that enables quantifying the amount of such a gas produced by gasoline engines equipped with catalytic converter.

Electromechanical characterization of piezoelectric polymer thin films in a broad frequency range

Abstract: Piezoelectric materials are usually characterized using resonant methods. However, piezoelectric polymers are used in broadband devices, thus requiring characterization over a wide range of frequencies. In this work, we present a non-resonant method for the broadband electromechanical characterization of piezoelectric polymer thin films. The procedure is based on measuring the complex capacitance of a sample of known geometry under three conditions: free, blocked and immersed in a fluid of known acoustic properties. The behaviour of the sample under study is modelled as a one-dimensional transducer and treated as a two-port network that relates the measurable electrical and mechanical variables. Also, the sample is considered as a free-space radiator when immersed in a fluid. The method determines the intensive and the equivalent circuit parameters of piezoelectric polymer films, allowing the characterization of elastic and electrical properties in a broad frequency range. In order to test the method, we performed isothermal capacitance measurements on a sample of poly(vinylidene fluoride) at a temperature of 298 K. The sample was measured along the direction of the poling field and in the frequency range from 10 Hz to 10 MHz. The results given by the method agree with those reported by other authors.

Strong size-dependent photoacoustic effect on gold nanoparticles: a sensitive tool for aggregation-based colorimetric protein detection

Abstract: Based on measuring the change of the photoacoustic (PA) signal generated by laser-induced nanobubbles, a new way to detect gold nanoparticles (GNPs) aggregation is demonstrated and applied to selective protein detection.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Abstract: A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Relative and absolute determination of fluorescence quantum yields of transparent samples

Abstract: Luminescence techniques are among the most widely used detection methods in the life and material sciences. At the core of these methods is an ever-increasing variety of fluorescent reporters (i.e., simple dyes, fluorescent labels, probes, sensors and switches) from different fluorophore classes ranging from small organic dyes and metal ion complexes, quantum dots and upconversion nanocrystals to differently sized fluorophore-doped or fluorophore-labeled polymeric particles. A key parameter for fluorophore comparison is the fluorescence quantum yield (Φf), which is the direct measure for the efficiency of the conversion of absorbed light into emitted light. In this protocol, we describe procedures for relative and absolute determinations of Φf values of fluorophores in transparent solution using optical methods, and we address typical sources of uncertainty and fluorophore class-specific challenges. For relative determinations of Φf, the sample is analyzed using a conventional fluorescence spectrometer. For absolute determinations of Φf, a calibrated stand-alone integrating sphere setup is used. To reduce standard-related uncertainties for relative measurements, we introduce a series of eight candidate quantum yield standards for the wavelength region of ∼350-950 nm, which we have assessed with commercial and custom-designed instrumentation. With these protocols and standards, uncertainties of 5-10% can be achieved within 2 h.

Photoacoustic imaging in biomedicine

Abstract: Photoacoustic imaging is a promising method for visualizing biological tissues with optical absorbers. This article provides an overview of the rapidly developing field of photoacoustic imaging. Photoacoustics, the physical basis of photoacoustic imaging, is analyzed briefly. The merits of photoacoustic technology, compared with optical imaging and ultrasonic imaging, are described. Various imaging techniques are also discussed, including scanning tomography, computed tomography and original detection of photoacoustic imaging. Finally, some biomedical applications of photoacoustic imaging are summarized.

Functionalized novel mesoporous adsorbent for selective lead(II) ions monitoring and removal from wastewater

Abstract: An efficient material is needed to develop selective and effective sensing/removal systems with high flexibility, and low capital cost for control the capturing of toxic ions. In this study, we designed ligand immobilized mesoporous adsorbent for ultra-trace Pb(II) monitoring and removal from wastewater. The adsorbent was synthesized by indirect immobilization of 4-tert-octyl-4-((phenyl)diazenyl)phenol onto inorganic mesoporous silica. This adsorbent exhibited the large surface area-to-volume ratios and uniformly shaped pores in case cavities, and its active sites kept open functionality to taking up Pb(II). The applicability of the adsorbent for Pb(II) detection and removal was assessed, and the efficient parameters such as solution pH, contacting time, initial Pb(II) concentration and ionic strength of competing ions were measured. The effective pH range for detection and removal systems was at the neutral region. The data revealed that the adsorbent was able to detect the ultra-trace Pb(II) ions with high sensitivity and selectivity by charge transfer (intense π–π transition) transduction mechanism. Then the adsorbent proved to have an efficient ability for continuous Pb(II) monitoring and removal even on-site and in situ chemical analyses. The maximum sorption capacity and limit of detection were 200.80 mg/g and 0.12 μg/L, respectively. The adsorbent was reused in several cycles without significant deterioration after elution with a suitable eluent (0.10 M HCl). Therefore, the design of mesoporous adsorbent has a great potentiality to be used in selective Pb(II) detection/removal from wastewater. Large-scale studies are recommended to confirm these promising results from the laboratory scale.

Fluorescence spectroscopy of Rhodamine 6G: concentration and solvent effects.

Abstract: Rhodamine 6G (R6G), also known as Rhodamine 590, is one of the most frequently used dyes for application in dye lasers and as a fluorescence tracer, e.g., in the area of environmental hydraulics. Knowing the spectroscopic characteristics of the optical emission is key to obtaining high conversion efficiency and measurement accuracy, respectively. In this work, solvent and concentration effects are studied. A series of eight different organic solvents (methanol, ethanol, n-propanol, iso-propanol, n-butanol, n-pentanol, acetone, and dimethyl sulfoxide (DMSO)) are investigated at constant dye concentration. Relatively small changes of the fluorescence spectrum are observed for the different solvents; the highest fluorescence intensity is observed for methanol and lowest for DMSO. The shortest peak wavelength is found in methanol (568 nm) and the longest in DMSO (579 nm). Concentration effects in aqueous R6G solutions are studied over the full concentration range from the solubility limit to highly dilute states. Changing the dye concentration provides tunability between ∼550 nm in the dilute case and ∼620 nm at high concentration, at which point the fluorescence spectrum indicates the formation of R6G aggregates.