Total internal reflection photoacoustic spectroscopy for the detection of β-hematin

Abstract

Abstract. Evanescent field sensing methods are currently used to detect many different types of disease markers and biologically important chemicals such as the HER2 breast cancer receptor. Hinoue et al. used Total Internal Reflection Photoacoustic Spectroscopy (TIRPAS) as a method of using the evanescent field to detect an optically opaque dye at a sample interface. Although their methods were successful at detecting dyes, the results at that time did not show a very practical spectroscopic technique, which was due to the less than typical sensitivity of TIRPAS as a spectroscopy modality given the low power (∼1 to 2 W) lasers being used. Contrarily, we have used an Nd:YAG laser with a five nanosecond pulse that gives peak power of 1 MW coupled with the TIRPAS system to increase the sensitivity of this technique for biological material sensing. All efforts were focused on the eventual detection of the optically absorbing material, hemozoin, which is created as a byproduct of a malarial infection in blood. We used an optically analogous material, β-hematin, to determine the potential for detection in the TIRPAS system. In addition, four properties which control the sensitivity were investigated to increase understanding about the sensor's function as a biosensing method.

Techniques and Challenges for Characterizing Metal Thin Films with Applications in Photonics

“…One such technique, Total Internal Reflection Photoacoustic Spectroscopy (TIRPAS), falls into the category of Evanescent Field-based Photoacoustics (EFPA) and has been demonstrated in the characterization of the thickness and refractive index of optically-transparent thin films [71]. Variations of the same technology have been suggested for use with metal and other optically-absorptive thin films, in the form of Surface Plasmon Resonance Photoacoustic Spectroscopy (SPRPAS) and Optical Tunneling Photoacoustic Spectroscopy (OTPAS), in addition to applications involving the detection of absorbing particles [38,72].…”

Evanescent Field Based Photoacoustics: Optical Property Evaluation at Surfaces

“…This family includes, but is not limited to, total internal reflection photoacoustic spectroscopy (TIRPAS), optical tunneling photoacoustic spectroscopy (OTPAS), and surface plasmon resonance photoacoustic spectroscopy (SPRPAS). The interested reader should refer to the following references for derivations of the equations used for TIRPAS 5,6,18,23,25,26,[33][34][35][43][44][45][46][47] , PAS/TIRPAS refractometry 18 , and OTPAS 6 . In each case, the photoacoustic effect is generated through a different excitation mechanism than simple transmittance through a prism; for instance, in TIRPAS, the light is evanescently coupled through a prism/substrate/sample interface into the chromophores (which could include the sample material itself, or guest molecules within the sample), whereas in SPRPAS, the primary mode of excitation is instead through the absorption of a surface plasmon, which is a secondary E-M wave created when the energy of the evanescent field is transferred into the electron cloud of a metal layer deposited on the prism surface.…”

“…That being said, a new set of techniques, known as evanescent field-based photoacoustics (EFPA) 5,6,15,18, as shown in Figure 1, has the potential to estimate material properties at the nanoscale in a consolidated set of experiments. EFPA encompasses the sub-techniques of total internal reflection photoacoustic spectroscopy (TIRPAS) 23,25,26,[33][34][35][43][44][45] , photoacoustic spectroscopy/total internal reflection photoacoustic spectroscopy refractometry (PAS/TIRPAS refractometry) /C p where α is the volume thermal expansion coefficient, v s is the speed of sound in the medium, and C p is the heat capacity at constant pressure, H 0 is the radiant exposure of the laser beam, c is the speed of sound in the excited medium, x is length, and t is time. The magnitude of the resulting acoustic wave relies directly upon the optical absorption coefficient of the material, µ a , which is the inverse of the optical penetration depth, δ, which is in turn a measure of the distance the light travels until it decays to 1/e of its initial optical intensity.…”

“…With such a small optical penetration depth, the evanescent field is able to interact with the environment very close to the interface of the two materials, and well below the optical and acoustic diffraction limits. The optical properties of materials or particles within this range may perturb the field or otherwise alter its generation, which interaction can be detected by a variety of methods 3,5,6,10,15,17,18,21,23,[25][26][27][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][84][85][86][87][88][89][90][91][92][93][94][95] .…”

“…More recently, previous investigations have shown that increased sensitivity and utility are possible with modern polyvinylidene fluoride (PVDF) ultrasonic detectors and q-switched neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers. Specifically, nanosecond-pulsed Nd:YAG lasers result in a 10 6 fold increase in the peak power, which enables EFPA techniques to become useful tools for evaluating the optical properties of a variety of materials and interfaces 5,6,15,18,[21][22][23][24][25][26][27][28][29][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]84,96 . Additionally, previous work has further shown the capability of such techniques to determine structural information about materials at an interface, which was previously never achievable with traditional photoacoustic spectroscopy (PAS) technologies due to their relatively large penetration depth 53,55,57,59,61,62,69,73,75,80,81 .…”