Comparison of coherent and spontaneous Raman microspectroscopies for noninvasive detection of single bacterial endospores

Abstract

Single bacterial spores were analyzed by using nonlinear Raman microspectroscopy based on coherent anti-Stokes Raman scattering (CARS). The Raman spectra were retrieved from CARS spectra and found to be in excellent agreement with conventionally collected Raman spectra. The phase retrieval method based on maximum entropy model revealed significant robustness to external noise. The direct comparison of signal amplitudes exhibited a factor of 100 stronger CARS signal, as compared with the Raman signal.microscopy ͉ nonlinear optics ͉ scattering stimulated ͉ ultrafast optics

The Dawn of Quantum Biophotonics

“…We have developed a new spectroscopic technique (FAST CARS) based on maximizing quantum coherence by breaking the adiabaticity** and laser pulse shaping to optimize it. In FAST CARS spectroscopy the signal is proportional to the number of molecules squared, as opposed to the linear dependence in the spontaneous Raman technique [14]. In addition, FAST CARS was the first proposal for background suppression in precision sensing of minor molecular species within a highly scattering environment [3], and provided an efficient solution to the problem of detecting and identifying anthrax-type bacterial endospores in real time [4,5].…”

Hyperspectral coherent anti-Stokes Raman scattering microscopy imaging through turbid medium

“…[1][2][3][4][5][6][7] Under proper excitation conditions, CARS microscopy and microspectroscopy is capable of providing a much stronger signal and has the potential for real-time chemical analysis of cells and tissues. 1,6,7 To make a quantitative chemical analysis possible, it is often necessary to collect the extended vibrational spectrum from a selected cell or tissue volume and use sophisticated mathematical algorithms to extract the required information. 8,9 While most of the research efforts are focused on optimizing experimental conditions for excitation and signal collection, we point that most of those efforts were concentrated on identifying objects either in thin samples, or in optically transparent media, thus limiting the area of applications of CARS microspectroscopy.…”

“…To illustrate the power of this approach, we first used two relatively simple examples for imaging, in which well-defined objects with strong Raman cross-section were imaged using single vibrational line CARS or Raman imaging and compared with images obtained through the hierarchical cluster analysis of hyperspectral data. After these validation tests, we utilized the same approach based on hierarchical cluster analysis to identify the presence of dipicolinic acid powder inside a paper envelope, which serves as a powerful example of chemically specific biological threat detection in the mail, since dipicolinic acid is the major compound of bacterial endospores accounting for up to 20% of their weight 7 ), and to identify the presence of microcalcifications by imaging and correctly identifying their chemical composition through a millimeter-thick skin layer. Microcalcification has been recognized as one of the potential markers for breast cancer, whose chemical composition has been linked to the grade of the pathological breast disease.…”

“…27), we found that it is possible to perform a hierarchical cluster analysis of collected CARS spectra to identify different chemical structures. After identifying different clusters, we employed a Raman retrieval procedure, which has been proven to provide an efficient way of converting information from CARS to Raman spectroscopic data, 7,8 to accurately identify chemical species in each cluster. To illustrate the power of this approach, we first used two relatively simple examples for imaging, in which well-defined objects with strong Raman cross-section were imaged using single vibrational line CARS or Raman imaging and compared with images obtained through the hierarchical cluster analysis of hyperspectral data.…”

Stimulated Raman photoacoustic imaging

“…Raman spectroscopy has long been considered for biological (18) and biomedical imaging (19). One of the shortcomings of Raman spectroscopy, its low quantum efficiency, has been successfully overcome by using its nonlinear optical analog, coherent anti-Stokes Raman scattering (CARS) microscopy, which has demonstrated its great potential for real-time microscopic imaging (20)(21)(22)(23). However, CARS microscopy in some versions requires optical phase-matching and is hardly applicable for imaging objects hidden deeply inside tissue.…”