Identification of biological microparticles using ultrafast depletion spectroscopy

Abstract

We show how an ultrafast pump-pump excitation induces strong fluorescence depletion in biological samples, such as bacteria-containing droplets, in contrast with fluorescent interferents, such as polycyclic aromatic compounds, despite similar spectroscopic properties. Application to the optical remote discrimination of biotic versus non-biotic particles is proposed. Further improvement is required to allow the discrimination of one pathogenic among other non-pathogenic micro-organisms. This improved selectivity may be reached with optimal coherent control experiments, as discussed in the paper.

Resolution of strongly competitive product channels with optimal dynamic discrimination: Application to flavins

“…47,48 Previous work has also established that ∼30% of the population excited into the S n manifold is irreversibly lost to this depletion channel. 3 Accordingly, such a population depletion induced by the IR pulse results in a decreased fluorescence signal from the S 1 state.…”

“…However, application of a time-delayed, unshaped pulse at 800 nm further excites the flavins to higher electronic states S n primarily via two-photon absorption. 3 Irreversible depletion of the S n manifold likely occurs through autoionizing states underlying the ∼220 nm absorption. Indeed, direct photoejection of electrons from the singlet manifold of aqueous-phase riboflavin has been observed following application of 253.7 nm radiation.…”

“…1 While bioaerosols such as tryptophan and riboflavin (RBF) share similar linear, static spectra with traffic-related urban hydrocarbon aerosols, the action of an ultrafast pump pulse and suitably time-delayed probe reveals distinct temporal responses that permit reliable discrimination. 2,3 Variation of the time-delay between the two pulses serves as a form of one-dimensional pulse shaping and is able to induce distinct temporal responses between the hydrocarbons and biological compounds. Nevertheless, a simple pump-probe scheme is unable to induce sufficiently disparate nonlinear responses amongst various flavins; in the present circumstance, nonlinear refers to the coordinated action of both the pump and probe pulses.…”

“…19,20 Such optimal dynamic discrimination (ODD) provides a means to transiently resolve the product channels of quantum systems with nearly indistinguishable initial states. The present work builds upon the one-parameter control of pump-repump schemes [1][2][3] and utilizes the full flexibility of adaptive, feedback pulse shaping to accomplish discrimination amongst cellular agents exhibiting nearly identical linear spectra.…”

Optimal Dynamic Discrimination in Tryptophan-Containing Dipeptides

“…Interestingly, even time-resolved approaches (i.e. fluorescence depletion), which proved successful in the past for discriminating trp-containing samples [1], are not selective enough in the present case. On the other hand, our group has demonstrated how, within the framework of Optimal Dynamic Discrimination (ODD) [2], a careful manipulation of pulse spectral-phase can drive the selective excitation of the low-frequency molecular modes in spectroscopycally identical biochromophores, eventually leading to their fluorescence-based identification in a mixture [2,3].…”