Membrane-protein systems constitute an important avenue for a variety of targeted therapies. The ability to alter these systems remotely via physical fields is highly desirable for the advance of noninvasive therapies. Biophysical action of acoustic fields in particular holds immense potential for applications in drug delivery and neuro-modulation. Here we investigate the optical response of solvato-chromic fluorescent probe Laurdan, embedded in multilamellar lipid vesicles, subjected to broadband pressure impulses of the order of 1Mpa peak amplitude and pulse width of less than 10 \mu%DIFDELCMD < }%%% s. The response is quantified in terms of the shift in fluorescence spectra using a ratiometric technique . Based on the fluctuation dissipation theorem applied to a coupled membrane-fluorophore system, it is shown that the perturbation of the fluorescence spectra of embedded molecules to the pressure impulses is determined by the thermodynamic state of the interface , or in other words, the thermodynamic susceptibilities such as the compressibility or heat capacity of the system. However, given that the thermodynamic susceptibilities of such systems, especially in native biological environment, are not easy to obtain experimentally, a necessary corollary to the thermodynamic approach is derived. This establishes a direct relation between the width of the emission spectra and the thermodynamic susceptibilities of the system. The result has practical importance as it gives access to the thermodynamic properties of the membrane from steady state fluorescence measurement without the need to perturb the system. Simply stated, the experiments show that the magnitude of the perturbation response of a membrane system to an acoustic insult is proportional to the width of the emission spectrum of the embedded membrane probe .
 %DIFDELCMD < }%%% Physical and chemical changes in biological interfaces can be quantified by corresponding changes in the thermodynamic state of the interface . Based on Einsteins approach to thermodynamics, we show that fluorescence spectra of a dye embedded in a lipid membrane is a function of the state of the interface . We derive the coupling between the energy fluctuations of a fluorophore and its environment allowing the thermodynamic susceptibility, in particular, the specific heat of the interface to be estimated from the spectra of the embedded fluorophore. The estimate of the thermodynamic susceptibility is shown to hold not only for quasi-static near-equilibrium measurements, but also for dynamic state changes in lipid vesicles induced by broadband pressure impulses of the order of 1 MPa peak amplitude and 10 microsecond pulse duration. These experiments also provide crucial insights into how dynamic state changes may affect biological function, for example, during an action potential or during therapeutic use of acoustic impulses in the form of ultrasound or shock waves .
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Membrane-protein systems constitute an important avenue for a variety of targeted therapies. The ability to alter these systems remotely via physical fields is highly desirable for the advance of noninvasive therapies. Biophysical action of acoustic fields in particular holds immense potential for applications in drug delivery and neuro-modulation. Here we investigate the optical response of solvato-chromic fluorescent probe Laurdan, embedded in multilamellar lipid vesicles, subjected to broadband pressure impulses of the order of 1Mpa peak amplitude and pulse width of less than 10
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\mu
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s. The response is quantified in terms of the shift in fluorescence spectra using a ratiometric technique
Physical and chemical changes in biological interfaces can be quantified by corresponding changes in the thermodynamic state of the interface
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the fluctuation dissipation theorem applied to a coupled membrane-fluorophore system, it is shown that the perturbation of the
Einsteins approach to thermodynamics, we show that
R
embedded molecules to the pressure impulses is determined by the thermodynamic
a dye embedded in a lipid membrane is a function of the
R
, or in other words, the thermodynamic susceptibilities such as the compressibility or heat capacity of
. We derive the coupling between the energy fluctuations of a fluorophore and its environment allowing the thermodynamic susceptibility, in particular,
R
system. However, given that the thermodynamic susceptibilities of such systems, especially in native biological environment, are not easy to obtain experimentally, a necessary corollary to the thermodynamic approach is derived. This establishes a direct relation between the width of the emission spectra and the thermodynamic susceptibilities of the system. The result has practical importance as it gives access to the thermodynamic properties of the membrane from steady state fluorescence measurement without the need to perturb the system. Simply stated, the experiments show that the magnitude of the perturbation response of a membrane system to an acoustic insult is proportional to the width of the emission spectrum of the embedded membrane probe
specific heat of the interface to be estimated from the spectra of the embedded fluorophore. The estimate of the thermodynamic susceptibility is shown to hold not only for quasi-static near-equilibrium measurements, but also for dynamic state changes in lipid vesicles induced by broadband pressure impulses of the order of 1 MPa peak amplitude and 10 microsecond pulse duration. These experiments also provide crucial insights into how dynamic state changes may affect biological function, for example, during an action potential or during therapeutic use of acoustic impulses in the form of ultrasound or shock waves