We introduce a hybrid technique that combines the robustness of frequency-resolved coherent anti-Stokes Raman scattering (CARS) with the advantages of time-resolved CARS spectroscopy. Instantaneous coherent broadband excitation of several characteristic molecular vibrations and the subsequent probing of these vibrations by an optimally shaped time-delayed narrowband laser pulse help to suppress the nonresonant background and to retrieve the species-specific signal. We used this technique for coherent Raman spectroscopy of sodium dipicolinate powder, which is similar to calcium dipicolinate (a marker molecule for bacterial endospores, such as Bacillus subtilis and Bacillus anthracis), and we demonstrated a rapid and highly specific detection scheme that works even in the presence of multiple scattering.

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Development of a phenotyping platform capable of noninvasive biochemical sensing could offer researchers, breeders, and producers a tool for precise response detection. In particular, the ability to measure plant stress in vivo responses is becoming increasingly important. In this work, a Raman spectroscopic technique is developed for high-throughput stress phenotyping of plants. We show the early (within 48 h) in vivo detection of plant stress responses. Coleus (Plectranthus scutellarioides) plants were subjected to four common abiotic stress conditions individually: high soil salinity, drought, chilling exposure, and light saturation. Plants were examined poststress induction in vivo, and changes in the concentration levels of the reactive oxygen-scavenging pigments were observed by Raman microscopic and remote spectroscopic systems. The molecular concentration changes were further validated by commonly accepted chemical extraction (destructive) methods. Raman spectroscopy also allows simultaneous interrogation of various pigments in plants. For example, we found a unique negative correlation in concentration levels of anthocyanins and carotenoids, which clearly indicates that plant stress response is fine-tuned to protect against stress-induced damages. This precision spectroscopic technique holds promise for the future development of high-throughput screening for plant phenotyping and the quantification of biologically or commercially relevant molecules, such as antioxidants and pigments.Raman spectroscopy | plant abiotic stress | carotenoids | anthocyanins W ith the global population projected to exceed 9 billion by the year 2050, the task of producing enough food and energy for the world is of utmost importance (1). In anticipation of rising food demand (2), the ability to measure plant stress in vivo is becoming increasingly vital for increasing agricultural production and research. For example, such technologies would allow a farmer to intervene on stress detection and also, make practical the development of crop varieties with increased tolerance to abiotic stress. The field environment requires a comprehensive and rapid screening technology for plant physiological, biochemical, and morphological characteristics (3). Such characteristics can be integrated to predict plant growth potential, biomass processibility, and abiotic stress responses before any visible signs occur in a plant. Plant growth is impacted by unseasonable droughts, cold, increased UV radiation and high-energy blue light associated with atmospheric changes in ozone levels, and fertilizer/irrigation application associated with increased soil salinity (4, 5). Most existing methods for evaluating biochemical characteristics use destructive chemical analyses, which require time and intensive labor. In addition, these methods use strong chemicals, which require special handling and disposal. Currently, in vivo sensing technologies are limited by the time required for detecting a stress response, the types of stress factors that can be detec...

We present a comparative analysis of spontaneous and coherent Raman scattering on pyridine. The instantaneous excitation of the molecular coherence is done by a pair of ultrashort preparation pulses. Then, a long narrowband probe pulse is scattered off the molecular vibrations. The described hybrid technique allows for the single-shot acquisition of a background-free coherent Raman spectrum within the excitation band and its straightforward comparison with the spontaneous Raman measurements, performed in the same setup. We report a 10(5)-fold increase in the efficiency of the Raman scattering process due to the broadband pump-Stokes preparation. The coherence magnitude (approximately 0.5x10(-3)) is inferred experimentally, without a priori knowledge about the molecular structure.