Optical Control Of Mass Ejection From Ferroelectric Liquid Droplets: A Possible Tool For The Actuation Of Complex Fluids

We report on the optical control of the recently observed electromechanical instability of ferroelectric liquid droplets exposed to the photovoltaic field of a lithium niobate ferroelectric crystal substrate. The ferroelectric liquid is a nematic liquid crystal in which almost complete polar ordering of the molecular dipoles generates an internal macroscopic polarization locally collinear to the mean molecular long axis. Upon entering the ferroelectric phase, droplets irradiated by unfocused beam undergo an electromechanical instability and disintegrate by the explosive emission of fluid jets. We show here that the regions of jets emission can be controlled by focusing the light beam in areas close to the droplet's edge. Once emitted, the fluid jets can be walked by moving the beam up to millimeter distance from the mother droplet. Reverting the lithium niobate substrate, jets become thinner and show the tendency of being repelled by the beam instead of being attracted, thus offering an additional tool for their optical manipulation. These observations may pave the way to intriguing applications of ferroelectric nematic fluids related to manipulation, actuation, and control of soft, flexible materials.Comment: 11 pages, 5 figure

Lithium niobate micromachining for the fabrication of microfluidic droplet generators

In this paper, we present the first microfluidic junctions for droplet generation directly engraved on lithium niobate crystals by micromachining techniques, preparatory to a fully integrated opto-microfluidics lab-on-chip system. In particular, laser ablation technique and the mechanical micromachining technique are exploited to realise microfluidic channels in T-and cross junction configurations. The quality of both lateral and bottom surfaces of the channels are therefore compared together with a detailed study of their roughness measured by means of atomic force microscopy in order to evaluate the final performance achievable in an optofluidic device. Finally, the microfluidics performances of these water-in-oil droplets generators are investigated depending on these micromachining techniques, with particular focus on a wide range of droplet generation rates

Local doping of lithium niobate by iron diffusion: a study of photorefractive properties

In the last decades the electronic data transmission technology has progressively reached its performance limits and it is nowadays evident that further advances can be achieved only by all-optical signal processing systems. Thus the research in nonlinear optics have been rapidly expanding in the last twenty years, developing many applications of photonics which are now relevant for industrial and consumer markets. In particular, in electro-optic materials the phenomena based on the photorefractive effect are doubtless playing a major role in the building up of optoelectronic signal transmission and processing devices and lithium niobate (LiNbO3) is a promising material due to its high electro-optic and nonlinear optical coefficients. Moreover, lithium niobate offers incredible versatility as substrate for integrated optics, allowing to realize on the same crystal optical elements with different functions, by exploiting various microstructural technologies. This kind of devices require the capability to locally change the physical properties of the material, by doping it with the proper element only in a limited area of the substrate. In particular, it is known that by doping the lithium niobate with iron the photorefractive properties of the material are enhanced, thus to realize an integrated optical system with a photorefractive stage an iron local doping has to be performed. In this work the thermal diffusion process is exploited to realize iron locally doped lithium niobate crystals and the structural and photorefractive properties of the doped layer are studied. In particular it has been designed and built-up a new optical set-up able to investigate only a limited area of the doped layer, thus allowing to relate at each depth the examined iron concentration with the corresponding photorefractive response of the material. In this way it is possible to realize in depth-profiles of the main physical photorefractive parameters involved in the photorefractive effect and physical mechanisms never studied before can be now investigated.Negli ultimi decenni la tecnologia di trasmissione di dati elettronici ha progressivamente raggiunto i suoi limiti di prestazione ed al giorno d'oggi è evidente che ulteriori sviluppi possono essere raggiunti solo con l'utilizzo di sistemi ottici integrati. Perciò la ricerca relativa all'ottica non lineare ha avuto una rapida espansione negli ultimi ventanni, sviluppando molte applicazioni fotoniche che risultano rilevanti sia per il mercato industriale che per quello privato. In particolare, tra i materiali elettro-ottici i fenomeni che si basano sull'effetto fotorifrattivo stanno senza dubbio avendo un ruolo importante nella realizzazione di dispositivi per la trasmissione e il trattamento di segnali optoelettronici e il niobato di litio (LiNbO3) è un materiale promettente, dati i suoi alti coefficienti elettro-ottici e ottici non lineari. Inoltre il niobato di litio offre un incredibile versatilità come substrato per ottiche integrate, permettendo di realizzare sullo stesso cristallo elementi ottici con differenti funzioni, sfruttando varie tecnologie di microstrutturazione. Questo tipo di dispositivi richiede la capacità di cambiare localmente le proprietà fisiche del materiale, drogandolo con un opportuno elemento su una regione limitata del substrato. In particolare, è noto che drogando il niobato di litio con ferro le proprietà fotorifrattive del material vengono notevolmente migliorate, così per realizzare un sistema ottico integrato che presenti uno stadio fotorifrattivo si deve realizzare un drogaggio locale con ferro. In questo lavoro il processo di diffusione termica è sfruttato per realizzare cristalli di niobato di litio drogati localmente con ferro e sono studiate le proprietà strutturali e fotorifrattive dello strato drogato. In particolare è stato sviluppato e costruito un apparato ottico in grado di investigare solo un'area limitata dello strato drogato, permettendo in tal modo ad ogni profondità all'interno della zona drogata di mettere in relazione la concentrazione di ferro esaminata con la corrispondente risposta fotorifrattiva del materiale. In questo modo è possibile realizzare profili in profondità delle principali grandezze fisiche coinvolte nell'effetto fotorifrattivo e meccanismi fisici mai studiati prima possono essere ora investigati

Force Dependence of Proteins’ Transition State Position and the Bell–Evans Model

Single-molecule force spectroscopy has opened a new field of research in molecular biophysics and biochemistry. Pulling experiments on individual proteins permit us to monitor conformational transitions with high temporal resolution and measure their free energy landscape. The force–extension curves of single proteins often present large hysteresis, with unfolding forces that are higher than refolding ones. Therefore, the high energy of the transition state (TS) in these molecules precludes kinetic rates measurements in equilibrium hopping experiments. In irreversible pulling experiments, force-dependent kinetic rates measurements show a systematic discrepancy between the sum of the folding and unfolding TS distances derived by the kinetic Bell–Evans model and the full molecular extension predicted by elastic models. Here, we show that this discrepancy originates from the force-induced movement of TS. Specifically, we investigate the highly kinetically stable protein barnase, using pulling experiments and the Bell–Evans model to characterize the position of its kinetic barrier. Experimental results show that while the TS stays at a roughly constant distance relative to the native state, it shifts with force relative to the unfolded state. Interestingly, a conversion of the protein extension into amino acid units shows that the TS position follows the Leffler–Hammond postulate: the higher the force, the lower the number of unzipped amino acids relative to the native state. The results are compared with the quasi-reversible unfolding–folding of a short DNA hairpin

Light controlled phase shifter for optofluidics

none4siopenopenL. Lucchetti; K. Kushnir; A. Zaltron; F. Simoni;Lucchetti, Liana; K., Kushnir; A., Zaltron; Simoni, Francesc

Opto-Microfluidic Integration of the Bradford Protein Assay in Lithium Niobate Lab-on-a-Chip

This paper deals with the quantification of proteins by implementing the Bradford protein assay method in a portable opto-microfluidic platform for protein concentrations lower than 1.4 mg/mL. Absorbance is measured by way of optical waveguides integrated to a cross-junction microfluidic circuit on a single lithium niobate substrate. A new protocol is proposed to perform the protein quantification based on the high correlation of the light absorbance at 595 nm, as commonly used in the Bradford method, with the one achieved at 633 nm with a cheap commercially available diode laser. This protocol demonstrates the possibility to quantify proteins by using nL volumes, 1000 times less than the standard technique such as paper-analytical devices. Moreover, it shows a limit of quantification of at least 0.12 mg/mL, which is four times lower than the last literature, as well as a better accuracy (98%). The protein quantification is obtained either by using one single microfluidic droplet as well by performing statistical analysis over ensembles of several thousands of droplets in less than 1 min. The proposed methodology presents the further advantage that the protein solutions can be reused for other investigations and the same pertains to the opto-microfluidic platform

Quantification of Iron (Fe) in Lithium Niobate by Optical Absorption

A quantitative method, based solely on optical absorption, to determine the total iron (Fe) concentration in Fe : LiNbO3 is proposed. Absorption spectra of several samples doped by thermal diffusion with different concentrations and different [Fe2+]/[Fe3+] ratios show an isosbestic point at 342 nm. At this wavelength the absorption is proportional to the total Fe concentration and does not depend on the oxidation state. Thanks to the large number of samples covering a wide range of concentrations, in this work it was possible to estimate an effective absorption cross-section relating the absorbance of a given sample to its iron content. The main advantage of the proposed method is in its simplicity and the fact that the result does not depend on the reduction degree of the sample. As it is known that the absorbance of Fe:LN at another wavelength (532 nm) gives information on the amount of Fe2+ present in the sample, our method makes it possible to characterize both the total Fe amount and its reduction degree within a single optical absorption measurement

Influence of iron doping on spatial soliton formation and fixing in lithium niobate crystals

We analyse the feasibility of using iron-doping in lithium niobate in order to stabilize and permanently fix light-induced integrated structures. General 3D optical interconnections were realized in bulk lithium niobate crystals by means of soliton waveguides exploiting the enhanced photorefractive properties obtainable using specific iron doping. We report an enhancement of the photorefractive properties in doped crystals that can be considered for permanently fixing the integrated circuits. This work opens new directions for realizing permanent self-assembled and self-aligned integrated electro-optic devices and photonic circuits