Quantum biophotonics : applications to plant stress and bacteria.

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Drought stress disrupts the balance of macro- and micronutrients and affects the yield of agriculturally and economically significant plants. Rapid detection of stress-induced changes of relative content of elements such as sodium (Na), potassium (K), calcium (Ca) and iron (Fe) in the field may allow farmers and crop growers to counter the effects of plant stress and to increase their crop return. Unfortunately, the currently available analytical methods are time-consuming, expensive and involve elaborate sample preparation which hinders routine daily monitoring of crop health on a field scale. An alternative method for rapid detection of drought stress in plants using femtosecond laser-induced breakdown spectroscopy (LIBS) is proposed. Daily monitoring of relative contents of Na, K, Ca and Fe in decorative indoor (gardenia) and cultivated outdoor (wheat) plant species under various degrees of drought stress is demonstrated. The observed differences in spectral and temporal responses indicate different mechanisms of drought resistance. Spectroscopic markers of drought stress which allow for distinguishing mild environmental and severe drought stress in wheat, may be used for remote field-scale estimation of plant stress resistance and health. Additionally, the ability to distinguish between crops and weeds using sensors from a distance will greatly benefit the farming community through improved and efficient scouting for weeds, reduced herbicide input costs and improved profitability. The utility of femtosecond LIBS for plant species differentiation is investigated. Greenhouse-grown plants of dallisgrass, wheat, soybean and bell pepper were evaluated using LIBS and elemental calcium transitions in plant tissue samples to measure plasma temperatures. Finally, Ultraviolet radiation is an effective bacterial inactivation technique with broad applications in environmental disinfection. However, biomedical applications are limited due to the low selectivity, undesired inactivation of beneficial bacteria and damage of healthy tissue. Here, the effects of aluminum nanoparticles prepared by sonication of aluminum foil on the ultraviolet inactivation of E. coli bacteria are investigated and demonstrate a new radiation protection mechanism via plasmonic nano-shielding. Direct interaction of the bacterial cells with the aluminum nanoparticles and elucidate the nano-shielding mechanism via ultraviolet plasmonic resonance and nanotailing effects are observed. The results provide a step towards developing improved radiation-based bacterial treatments.

Biophotonics. Plant stress. Plasma temperature. LIBS.