In-Line Ultrasound-Enhanced Raman Spectroscopy Allows for Highly Sensitive Analysis with Improved Selectivity in Suspensions

Abstract

Raman spectroscopy is a nondestructive characterization method offering chemical-specific information. However, the cross-section of inelastically (Raman) scattered light is very low compared to elastically (Rayleigh) scattered light, resulting in weak signal intensities in Raman spectroscopy. Despite providing crucial information in off-line measurements, it usually is not sensitive enough for efficient, in-line process control in conjunction with low particle concentrations. To overcome this limitation, two custom-made 1.4404 stainless-steel prototype add-ons were developed for in-line Raman probes that enable ultrasound particle manipulation and thus concentration of particles in suspensions in the focus of the Raman excitation laser. Depending on size and density differences between particles and the carrier medium, particles are typically caught in the nodal planes of a quasi-standing wave field formed in an acoustic resonator in front of the sensor. Two arrangements were realized with regard to the propagation direction of the ultrasonic wave relative to the propagation direction of the laser. The parallel arrangement improved the limit of detection (LOD) by a factor of ≈30. In addition to increased sensitivity, the perpendicular arrangement offers increased selectivity: modifying the frequency of the ultrasonic wave field allows the liquid or solid phase to be moved into the focus of the Raman laser. The combination of in-line Raman spectroscopy with ultrasound particle manipulation holds promise to push the limits of conventional Raman spectroscopy, hence broadening its field of application to areas where previously Raman spectroscopy has not had sufficient sensitivity for accurate, in-line detection.

Monitoring E. coli Cell Integrity by ATR-FTIR Spectroscopy and Chemometrics: Opportunities and Caveats

“…This is a disadvantage of ATR-FTIR compared to Raman spectroscopy [17], although the spectral contribution of biomass is higher for conventional Raman spectroscopy, and probe modifications are required to ensure the separation of cells and medium. This was recently achieved with synthetic particles by ultrasound-enhanced in-line probes [46], but applicability to E. coli cells has not yet been shown. The strong absorption of medium components and their spectral overlap with lysed cells was another potential obstacle in the present work.…”

Quantitative evaluation of light distribution in skin tissue for short-pulsed laser treatment using Monte Carlo simulation combined with nonlinear absorption model of melanin

“…Furthermore, nonlinear scattering is also negligible because its intensity is weaker than that of linear scattering in the power density used in this study. 14,15 The resulting fluence distribution takes into account nonlinear absorption by melanin. Figure 2(a) shows the nonlinear absorption model of melanin based on a simplified Jablonski three-level diagram consisting of the ground state (S 0 ), the first excited state (S 1 ), and the second excited state (S 2 ).…”

Greener organic synthetic methods: Sonochemistry and heterogeneous catalysis promoted multicomponent reactions

“…Ultrasound is characterized as any sound wave in frequencies above the normal hearing range of the human ear (i.e., above 16 kHz) [14] and the field of application of ultrasonic waves is surprisingly vast, such as in the pharmaceutical and food industries [15] , [16] , [17] , [18] , [19] , [20] , extraction processes [16] , [21] , [22] , [23] , [24] , [25] , [26] , [27] , [28] , [29] , [30] , [31] , waste treatment [32] , [33] , [34] , [35] , [36] , [37] , [38] , [39] , [40] , [41] , [42] , [43] , [44] , [45] , [46] , materials chemistry [47] , [48] , [49] , analytical chemistry [50] , [51] , [52] , [53] , and nanoparticle synthesis [24] , [41] , [54] , [55] , [56] , [57] , [58] , [59] . All these examples, addressing the application of ultrasound for different purposes, serve as consolidating pillars for the importance of this tool for the progress of science and technology.…”