Characterization of Nitrazine Yellow as a Photoacoustically Active pH Reporter Molecule

Abstract

Throughout the fields of biomedical imaging, materials analysis, and routine chemical analysis, it is desirable to have a toolkit of molecules that can allow noninvasive/remote chemical sensing with minimal sample preparation. Here, we describe the photophysical properties involved in photoacoustic (PA) measurements and present a detailed analysis of the requirements and complications involved in PA sensing. We report the use of nitrazine yellow (NY) as a well-behaved PA pH reporter molecule. Both the basic and acidic forms of NY are photoacoustically well-behaved and allow for rapid and noninvasive measurement of pH in either transparent or turbid media. We also find that the serum protein-bound form of NY is photoacoustically well-behaved and should permit applications in noninvasive 3D imaging (e.g., the lymphatic system).

Characterization of Reversibly Switchable Fluorescent Proteins in Optoacoustic Imaging

“…Exemplary wave functions of our optoacoustic signal can be found in Supporting Information ( Figure S4). The waveform is virtually identical, so no other heat realizing process take place on the time scale of our transducer detection 34,35 . We further show this data in frequency space ( Figure S5) showing the same result with major contributions from frequencies around 0.3 MHz.…”

Challenging a preconception: Optoacoustic spectrum differs from the absorption spectrum of proteins and dyes for molecular imaging

“…P. McGlynn, 1969;Schaberle et al, 2016). Thus, in order to accurately compare different optoacoustic capacities, the OAS has to be normalized by the absorbance, so that the slope of the linear relation between the OAS and absorbance yields the photoacoustic generation efficiency (PGE), which is a measure of how much of the absorbed energy is converted to pressure (Abbruzzetti et al, 1999;Braslavsky et al, 1983a;Brown et al, 2015;Laufer et al, 2013;Rosencwaig, 1980). As mentioned before, photostability and the lack of any fluorescence make BBN an ideal reference for photoacoustic measurements; accordingly, we assign it a PGE value of 1.0, assuming that no other decay channels take place (Abbruzzetti et al, 1999;Brown et al, 2015).…”

“…Importantly, BBN, in contrast to NiCl2, is soluble and stable in aqueous buffer solutions. BBN thus shares a common Grüneisen parameter [16][17][18] with labels for in vivo imaging, which are frequently dissolved in aqueous buffer systems. The combination of the excellent solubility of BBN and its stable generation of OA signals over a range of concentrations and excitation energies makes it well suited to serve as a universal standard for precise and reproducible OA measurements.…”

“…All of these processes reduce the number of available electrons that can undergo vibrational relaxation and produce a change in pressure in the time scale that the transducers and the illumination pulse length used in imaging devices can detect [21][22][23] . Thus, in order to accurately compare different optoacoustic capacities, the OAS has to be normalized by the absorbance, so that the slope of the linear relation between the OAS and absorbance yields the photoacoustic generation efficiency (PGE), which is a measure of how much of the absorbed energy is converted to pressure 12,17,18,24,25 .…”

“…As is shown in equation 3, the PGE is attenuated by fluorescence ( 01 ) and any other competitive pathway (X). As mentioned before, photostability and lack of any fluorescence make BBN an ideal reference for photoacoustic measurements; accordingly, we assign it a PGE value of 1.0, assuming that no other decay channels take place 17,18 .…”