We analyze the equations governing the evolution of distributions of the work and the heat exchanged with the environment by a manipulated stochastic system, by means of a compact and general derivation. We obtain explicit solutions for these equations for the case of a dragged Brownian particle in a harmonic potential. We successfully compare the resulting predictions with the outcomes of experiments, consisting in dragging a micron-sized colloidal particle through water with a laser trap. The study of the physics of small systems has recently received a boost by the possibility of manipulating nanosystems and biomolecules. The fluctuations of the work and heat that these small systems exchange with the environment while being manipulated can be of the order or even larger than the thermal energy, leading to "transient" violations of the second principle of thermodynamics. The distributions of heat and work have been experimentally studied for a few brownian systems [1,2,3,4]. The probability distribution function (PDF) of the work done on a Brownian particle dragged by a moving quadratic potential was derived in [5,6]. The distribution turns out to be gaussian, what has been taken as an ansatz in [6] and confirmed in [7] by means of a rather involved path integral calculation. On the other hand, obtaining the PDF of the transferred heat represents a much more difficult task: the Fourier transform of this function was obtained in refs. [6,7] by exploiting the energy balance and the gaussian ansatz for the work PDF, valid when the potential is quadratic.In the present paper we derive in a simple way the differential equations governing the evolution of the PDFs of the work and heat exchanged by a brownian particle, valid for any choice of the potential acting on the particle. The solutions of these equation turn out to fulfill the well-known fluctuation relations. We evaluate the solution of these equations for a moving harmonic potential. We then experimentally study the work and the heat exchanged by a colloidal particle dragged through water by an optical trap. The PDF's predicted by our equations result in an excellent agreement with the experimental data. We were inspired by the experiment of Wang et al. [1] where the work done on a similar system was measured. However, in that experiment, only the performed work, and not the heat transferred, was sampled. Moreover, the expected gaussian distribution of the performed work was not verified, and a detailed comparison with the theoretical predictions was not attempted. However in a subsequent paper [8], the authors stressed that the PDF of the work has to be gaussian in their experimental conditions. Let us consider a Brownian particle in the overdamped regime, driven by a time-dependent potential U (x, X(t)), where X is an externally controlled parameter, that varies according to a fixed protocol X(t). The Langevin equation is given bywhere f (t)f (t ′ ) = (2Γ/β)δ(t − t ′ ) and the prime denotes derivative with respect to x. We have defined β = (k B T ) −1 , ...

In this work, the effects of thalassemia, a blood disease quite diffuse in the Mediterranean sea region, have been investigated at single cell level using a Raman Tweezers system. By resonant excitation of hemoglobin Raman bands, we have examined the oxygenation capability of beta-thalassemic erythrocytes. A reduction of this fundamental erythrocyte function has been found. The measurements have been performed on a significant number of red blood cells; the relative statistical analysis is presented. Moreover, the response to photo-induced oxidative stress of diseased cells with respect to the normal ones has been analyzed. Finally, the deformability of thalassemic erythrocytes has been quantified by measuring the membrane shear modulus by using a double-trap system: the measurements have revealed an increase in membrane rigidity of more than 40%, giving evidence that the genetic defect associated to thalassemia, which manly relies on hemoglobin structure, also strongly affects the erythrocyte mechanical properties. Our results demonstrate that the developed set-up may have potential for the monitoring of blood diseases and their response to drug therapies.

Label-free chemical imaging of live cell membranes can shed light on the molecular basis of cell membrane functionalities and their alterations under membrane-related diseases. In principle, this can be done by surface-enhanced Raman scattering (SERS) in confocal microscopy, but requires engineering plasmonic architectures with a spatially invariant SERS enhancement factor G(x, y) = G. To this end, we exploit a self-assembled isotropic nanostructure with characteristics of homogeneity typical of the so-called near-hyperuniform disorder. The resulting highly dense, homogeneous and isotropic random pattern consists of clusters of silver nanoparticles with limited size dispersion. This nanostructure brings together several advantages: very large hot spot density (∼10(4) μm(-2)), superior spatial reproducibility (SD < 1% over 2500 μm(2)) and single-molecule sensitivity (Gav ∼ 10(9)), all on a centimeter scale transparent active area. We are able to reconstruct the label-free SERS-based chemical map of live cell membranes with confocal resolution. In particular, SERS imaging is here demonstrated on red blood cells in vitro in order to use the Raman-resonant heme of the cell as a contrast medium to prove spectroscopic detection of membrane molecules. Numerical simulations also clarify the SERS characteristics of the substrate in terms of electromagnetic enhancement and distance sensitivity range consistently with the experiments. The large SERS-active area is intended for multi-cellular imaging on the same substrate, which is important for spectroscopic comparative analysis of complex organisms like cells. This opens new routes for in situ quantitative surface analysis and dynamic probing of living cells exposed to membrane-targeting drugs.

The forces acting on an optically trapped particle are usually assumed to be conservative. However, the presence of a non-conservative component has recently been demonstrated. Here we propose a technique that permits one to quantify the contribution of such a non-conservative component. This is an extension of a standard calibration technique for optical tweezers and, therefore, can easily become a standard test to verify the conservative optical force assumption. Using this technique we have analyzed optically trapped particles of different size under different trapping conditions. We conclude that the non-conservative effects are effectively negligible and do not affect the standard calibration procedure, unless for extremely low-power trapping, far away from the trapping regimes usually used in experiments.