A Novel Methodology for Detecting Variations in Cell Surface Antigens Using Cell-Tearing by Optical Tweezers

The quantitative analysis of cell surface antigens has attracted increasing attention due to the antigenic variation recognition that can facilitate early diagnoses. This paper presents a novel methodology based on the optical "cell-tearing" and the especially proposed "dilution regulations" to detect variations in cell surface antigens. The cell attaches to the corresponding antibody-coated slide surface. Then, the cell-binding firmness between a single cell and the functionalized surface is assayed by optically tearing using gradually reduced laser powers incorporated with serial antibody dilutions. Groups B and B3 of red blood cells (RBCs) were selected as the experiment subject. The results indicate that a higher dilution called for lower power to tear off the cell binding. According to the proposed relative-quantitative analysis theory, antigenic variation can be intuitively estimated by comparing the maximum allowable dilution folds. The estimation result shows good consistency with the finding in the literature. This study suggests a novel methodology for examining the variation in cell surface antigens, expected to be widely capable with potential sensor applications not only in biochemistry and biophysics, but also in the micro-/nano- engineering field.

3D Printing and Pyrolysis of Optical ZrO2 Nanostructures by Two-Photon Lithography: Reduced Shrinkage and Crystallization Mediated by Nanoparticles Seeds

Two-photon lithography is a potential route to produce high-resolution 3D ceramics. However, the large shrinkage due to the elimination of an important organic counterpart of the printed material during debinding/sintering remains a lock to further development of this technology. To limit this phenomenon, an original approach based on a composite resin incorporating 45 wt% ultrasmall (5 nm) zirconia stabilized nanoparticles into the zirconium acrylate precursor is proposed to process 3D zirconia microlattices and nanostructured optical surfaces. Interestingly, the nanoparticles are used both as seeds allowing control of the crystallographic phase formed during the calcination process and as structural stabilizing agent preventing important shrinkage of the printed ceramic. After 3D photolithography and pyrolysis, the weight and volume loss of the microstructures are drastically reduced as compared to similar systems processed with the reference resin without nanoparticles, and stable 3D microstructures of cubic zirconia are obtained with high spatial resolution. In the case of a patterned surface, the refractive index of 2.1 leads to a diffraction efficiency large enough to obtain microfocusing with linewidths of 0.1 µm, and the demonstration of a microlens array with a period as small as 0.8 µm.

Correction: Laser-induced cross-linking GFP-AcmA′ bioprobe for screening Gram-positive bacteria on a biochip

Correction for ‘Laser-induced cross-linking GFP-AcmA′ bioprobe for screening Gram-positive bacteria on a biochip’ by Chuen-Fu Lin et al., RSC Adv., 2014, 4, 62882–62887.

Plasmonic bipyramids for fluorescence enhancement and protection against photobleaching

A great number of studies focus their interest on the photophysical properties of fluorescent hybrid gold nanoparticles for potential applications in biotechnologies such as imaging and/or treatment. Spherical gold nanoparticles are known to quench a chromophore fluorescent signal, when moieties are located in their close vicinity. The use of a polymer spacer on such a system allowed only partial recovery of the dye emission by controlling the surface to dye distance. Gold-based anisotropic sharp nanostructures appear to exhibit more interesting features due to the strong electric field generated at their edges and tips. In this paper, a complete study of hybrid fluorescent bipyramidal-like gold nanostructures is presented. We describe the chemical synthesis of gold bipyramids functionalized with fluorescent water-soluble polymers and their photophysics both in solution and on a single object. We show that the use of a bipyramidal shape instead of a spherical one leads to total recovery of the fluorescence and even to an enhancement of the emission of the dyes by a factor of 1.4.

Tuning dye-to-particle interactions toward luminescent gold nanostars

Light-matter interactions are of great interest for potential biological applications (bioimaging, biosensing, phototherapy). For such applications, sharp nanostructures exhibit interesting features since their extinction bands (surface plasmon resonance) cover a large bandwidth in the whole visible wavelength region due to the existence of "hot spots" located at the end of the tips. In this context, gold nanostars appear to be interesting objects. However, their study remains difficult, mainly due to complicated synthetic methods and further functionalization. This paper reports the synthesis, functionalization, and photophysics of luminescent hybrid gold nanostars prepared using a layer-by-layer (LbL) deposition method for the tuning of chromophore-to-particle distances together with the impact of the spectral overlap between the plasmon and the emission/absorption of the dyes. Several luminescent dyes with different optical signatures were selectively adsorbed at the nanoparticle surface. The optimized systems, exhibiting the highest luminescence recovery, clearly showed that overlap must be as low as possible. Also, the fluorescence intensities were quenched in close vicinity of the metal surface and revealed a distance-dependence with almost full recovery of the dyes emission for 11 LbL layers, which corresponded to 15 nm distances evaluated on dried samples. The photophysics of the luminescent core-shell particles were carried out in suspension and correlated with the response of isolated single objects.

Nanocarriers with ultrahigh chromophore loading for fluorescence bio-imaging and photodynamic therapy

We describe the design of original nanocarriers that allows for ultrahigh chromophore loading while maintaining the photo-activity of each individual molecule. They consist in shells of charged biocompatible polymers grafted on gold nanospheres. The self-organization of extended polymer chains results from repulsive charges and steric interactions that are optimized by tuning the surface curvature of nanoparticles. This type of nano-scaffolds can be used as light-activated theranostic agents for fluorescence imaging and photodynamic therapy. We demonstrate that, labeled with a fluorescent photosensitizer, it can localize therapeutic molecules before triggering the cell death of B16-F10 melanoma with an efficiency that is similar to the efficiency of the polymer conjugate alone, and with the advantage of extremely high local loading of photosensitizers (object concentration in the picomolar range).

Synthesis of PEGylated gold nanostars and bipyramids for intracellular uptake

A great number of works have focused their research on the synthesis, design and optical properties of gold nanoparticles for potential biological applications (bioimaging, biosensing). For this kind of application, sharp gold nanostructures appear to exhibit the more interesting features since their surface plasmon bands are very sensitive to the surrounding medium. In this paper, a complete study of PEGylated gold nanostars and PEGylated bipyramidal-like nanostructures is presented. The nanoparticles are prepared in high yield and their surfaces are covered with a biocompatible polymer. The photophysical properties of gold bipyramids and nanostars, in suspension, are correlated with the optical response of single and isolated objects. The resulting spectra of isolated gold nanoparticles are subsequently correlated to their geometrical structure by transmission electron microscopy. Finally, the PEGylated gold nanoparticles were incubated with melanoma B16-F10 cells. Dark-field microscopy showed that the biocompatible gold nanoparticles were easily internalized and most of them localized within the cells.

Metallic nanowires can lead to wavelength-scale microlenses and microlens arrays

We theoretically and experimentally demonstrate that the diffraction of microstructures based on silver nanowires leads to very efficient microfocusing effects. Pairs of parallel nanowires act as ultrasmall cylindrical microlenses with diffraction-limited resolution in the Fresnel region. This is a new diffraction scheme to make micron-sized optical lenses with higher transmittance than plasmonic microlens based on nano-aperture arrays. Calculations based on the scalar Rayleigh-Sommerfeld integral highlights the pure scalar diffractive contribution. Thus, the plasmon contribution is negligible in such micron-sized metallic geometry. We demonstrate that two-dimensional grids of nanowires can be used to fabricate dense arrays of microlenses, i.e. 10000x10000 DPI (dots per inch).

Influence of bromine substitution pattern on the singlet oxygen generation efficiency of two-photon absorbing chromophores

A molecular engineering strategy based on rational variations of the bromine substitution pattern in two-photon absorbing singlet oxygen sensitizers allows studying the relations that exist between the positioning of an inter-system crossing promoter on the charge-transfer chromophore and its ability to generate singlet oxygen.

Multiplying optical tweezers force using a micro-lever

This study presents a photo-driven micro-lever fabricated to multiply optical forces using the two-photon polymerization 3D-microfabrication technique. The micro-lever is a second class lever comprising an optical trapping sphere, a beam, and a pivot. A micro-spring is placed between the short and long arms to characterize the induced force. This design enables precise manipulation of the micro-lever by optical tweezers at the micron scale. Under optical dragging, the sphere placed on the lever beam moves, resulting in torque that induces related force on the spring. The optical force applied at the sphere is approximately 100 to 300 pN, with a laser power of 100 to 300 mW. In this study, the optical tweezers drives the micro-lever successfully. The relationship between the optical force and the spring constant can be determined by using the principle of leverage. The arm ratio design developed in this study multiplies the applied optical force by 9. The experimental results are in good agreement with the simulation of spring property.

Chitosan-coated triangular silver nanoparticles as a novel class of biocompatible, highly effective photothermal transducers for in vitro cancer cell therapy

One of the relevant directions that nanotechnology is taking nowadays is connected with nanomedicine and specifically related to the use of light and nanoparticles in early diagnosis and effective therapeutics of cancer. Noble-metal nanoparticles can act under laser irradiation as effective photothermal transducers for triggering localized hyperthermia of tumors. In this work we report the performance of newly synthesized chitosan-coated silver nanotriangles (Chit-AgNTs) with strong resonances in near-infrared (NIR) to operate as photothermal agents against a line of human non-small lung cancer cells (NCI-H460). The hyperthermia experiments were conducted by excitation of nanoparticles-loaded cells at 800 nm wavelength from a Ti:Sapphire laser. We found that the rate of cell mortality in the presence of Chit-AgNTs is higher than in the presence of thiolated poly(ethylene) glycol capped gold nanorods (PEG-AuNRs) - a common hyperthermia agent used as reference-, while no destructive effects were noticed on the control sample (cells without nanoparticles) under identical irradiation conditions. Additionally, we conducted cytotoxicity assays and found Chit-AgNTs to be efficiently uptaken by the cells while exhibiting good biocompatibility for healthy human embryonic cells (HEK), which is essential for any in vivo applications. Our results reveal a novel class of biocompatible plasmonic nanoparticles with high potential to be implemented as effective phototherapeutic agents in the battle against cancer.

Transparent plasmonic nanocontainers protect organic fluorophores against photobleaching

Numerous research efforts are investigating the possibility of using light interactions with metallic nanoparticles to improve the fluorescence properties of nearby molecules. Few investigations have considered the encapsulation of molecules in metallic nanocavities. In this paper, we present the optical properties of new hybrid nanoparticles consisting of gold nanoshells and fluorescent organic dyes in their liquid cores. Microspectroscopy on single nanoparticle demonstrates that the extinction spectra are in good agreement with Mie's theory. Finite difference time domain (FDTD) calculations reveal that excitation and emission radiations are efficiently transmitted through the thin gold nanoshells. Thus, they can be considered as transparent plasmonic nanocontainers for photoactive cores. In agreement with FDTD calculations, measurements show that fluorophores encapsulated in gold nanoshells keep their brightness, but they show fluorescence lifetimes 1 order of magnitude shorter. As a salient consequence, the photoresistance of encapsulated organic dyes is also improved by an order of magnitude. This unusual ultraviolet photoresistance results from the reduced probability of triplet-singlet conversion that eventually exposes dyes to singlet oxygen photodegradation.

Optically driven Archimedes micro-screws for micropump application

Archimedes micro-screws have been fabricated by three-dimensional two-photon polymerization using a Nd:YAG Q-switched microchip laser at 532nm. Due to their small sizes they can be easily manipulated, and made to rotate using low power optical tweezers. Rotation rates up to 40 Hz are obtained with a laser power of 200 mW, i.e. 0.2 Hz/mW. A photo-driven micropump action in a microfluidic channel is demonstrated with a non-optimized flow rate of 6 pL/min. The optofluidic properties of such type of Archimedes micro-screws are quantitatively described by the conservation of momentum that occurs when the laser photons are reflected on the helical micro-screw surface.

Degenerate multi-photon properties of spirofluorene derivatives

Two- and three-photon absorption properties of the fluorene-based chromophores have been investigated. The two- and three-photon absorption cross-section are found to be increased with the strength of the electron donor groups in the order of N-ethylcarbazoyl (1), triphenylamino (2), and N,N-dibutylanilino (3) groups. This nonlinear absorption enhancement can be interpreted by the increase of intramolecular charge transfer facilitated by strong electron donors and the decreased detuning energy (deltaE). Furthermore, direct laser microfabrication by two-photon photopolymerization with compound 2 as a two-photon sensitizer was carried out. Laser exposure time-dependent lateral voxel size has also been studied.

Gold hollow spheres obtained using an innovative emulsion process: towards multifunctional Au nanoshells

The tremendous development of materials with fine tuning of their composition, shape, size and chemical functionalities at the nanometer scale has opened a wide range of applications, particularly in medicine. Metallic nanoparticles are extremely interesting for such developments. The fundamental study of surface plasmon resonance (SPR) versus the shape/size of a particle is an important challenge. In this field, we propose a synthetic strategy using an original biphasic emulsion process linked to chemo-reduction of gold salt HAuCl(4). This method allows the preparation of new functional nanocapsules. These nanomaterials are fully characterized.

Two-Photon Microscopy and Spectroscopy of Lanthanide Bioprobes

The linear and non-linear photophysical properties of tris-dipicolinate europium and terbium complexes (absorption, emission, lifetime, luminescence induced by two-photon absorption) are studied in the crystalline state as well as in protein derivative crystals and compared to those in solution. Upon laser irradiation at 532 nm, luminescence of terbium is induced by a two-photon antenna effect, whereas luminescence of europium results from one-photon absorption in forbidden f-f transitions. Finally, linear and two-photon microscopy imaging experiments on biological and bio-inspired crystals are performed. These first proof-of-concept experiments open the way for the development of time-resolved non-linear microscopy that should combine the advantages of lanthanide luminescence (long lifetime, sharp emission bands, insensitivity to oxygen) with those of confocal biphotonic excitation (near-IR excitation, 3D resolution and reduced photodamage).

Conjugation of a New Two-Photon Fluorophore to Poly(ethylenimine) for Gene Delivery Imaging

We report herein the molecular engineering of an efficient two-photon absorbing (TPA) chromophore based on a donor-donor bis-stilbenyl entity to allow conjugation with biologically relevant molecules. The dye has been functionalized using an isothiocyanate moiety to conjugate it with the amine functions of poly(ethylenimine) (PEI), which is a cationic polymer commonly used for nonviral gene delivery. Upon conjugation, the basic architecture and photophysical properties of the active TPA chromophore remain unchanged. At the usual N/P ratio (ratio of the PEI positive charges to the DNA negative charges) of 10 used for transfection, the transfection efficiency and cytotoxicity of the labeled PEI/DNA complexes were found to be comparable to those of the unlabeled PEI/DNA complexes. Moreover, when used in combination with unlabeled PEI (at a ratio of 1 labeled PEI to 3 unlabeled PEI), the labeled PEI does not affect the size of the complexes with DNA. The labeled PEI was successfully used in two-photon fluorescence correlation spectroscopy measurements, showing that at N/P = 10 most PEI molecules are free and the diffusion coefficient of the complexes is consistent with the 360 nm size measured by quasielastic light scattering. Finally, two-photon images of the labeled PEI/DNA complexes confirmed that the complexes enter into the cytoplasm of HeLa cells by endocytosis and hardly escape from the endosomes. As a consequence, the functionalized TPA chromophore appears to be an adequate tool to label the numerous polyamines used in nonviral gene delivery and characterize their complexes with DNA in two-photon applications.

Two-Photon Antenna Effect Induced in Octupolar Europium Complexes

The synthesis of new chromophore-based pyridine-dicarboxamide ligands and related D3 symmetric europium(III) complexes is described. The photophysical properties of the ligands and the complexes were thoroughly investigated and interpreted on the basis of theoretical calculations (TD-DFT). Finally, the luminescence of Eu(III) was sensitized by two-photon absorption of the ligand, illustrating the two-photon antenna effect phenomenon.

Diarylethene microcrystals make directional jumps upon ultraviolet irradiation

Microcrystals of a diarylethene {1,2-bis[5'-methyl-2'-(2"-pyridyl)thiazolyl]perfluorocyclo-pentene} undergo jumps upon photoirradiation. These photochromic crystals present molecular structural changes upon irradiation with ultraviolet light because of reversible photocyclization reactions. When the energy absorbed by crystals reaches about 10 microJ, the uniaxial stress induced in the crystal lattice relaxes through directional jumps. If one prevents crystals from jumping, then parallel, equidistant cracks appear on crystal surfaces. These photomechanical effects could result from a Grinfeld surface instability.

Novel ruthenium(ii) and zinc(ii) complexes for two-photon absorption related applications

Two new fluorene derivatized 1,10-phenanthroline ligands and related tris-chelate Ru(II) or Zn(II) coordination complexes have been synthesised. The linear and nonlinear (two-photon induced fluorescence) photophysical measurements have contributed to highlight the possibility to tune the absorption spectral range and excited lifetime, depending on ligand substitution and nature of the metal. More significantly, the observation of two-photon absorption (TPA) associated with long-lived metal-to-ligand charge-transfer (MLCT) excited states in the Ru(II)-based chromophores, opens a wide range of applications in the near infrared.

Synthesis of chromophores combining second harmonic generation and two photon induced fluorescence properties

The design of new chromophores presenting simultaneous SHG and TPEF properties is reported.

Synthesis, Characterization, and UV−vis Linear Absorption of Centrosymmetric π-Systems Incorporating closo-Dodecaborate Clusters

Single- and multibranched centrosymmetric derivatives incorporating B12 clusters [B12H11-N(H)=C(H)-C6H4-C6H4-C(H)=(H)N-B12H11]2- (3) and [1,3,5-(4-(B12H11-N(H)=C(H))-C6H4)-C6H3]3- (5) have been synthesized. Both derivatives were characterized by multinuclear NMR and ESI-MS analyses. To the best of our knowledge, compound 5 is the first example of a multicage derivative bearing three B12 units. Compounds 3 and 5 are only slightly yellowish colored. The UV-vis absorption curves of 3 and 5 show intense absorption bands at 360 and 314 nm, respectively. This result permits us to confirm the strong donor effect of the B12 cluster. The hypsochrome effect observed for compound 5 compared to that of compound 3 confirms the interest in multibranched derivatives for the preparation of two-photon absorption materials active in the visible range.

Velocimetry microsensors driven by linearly polarized optical tweezers

We report on a new type of single-point velocimetry microsensor that can be positioned in microfluidic devices by use of optical tweezers. The flag-shaped microsensor is readily made by a low-cost two-photon polymerization technique. At rest the linearly polarized optical tweezer traps the microsensor at the focal point, and the flag-plate gets aligned in the polarization direction. Under a fluid flow, the plate rotates to an equilibrium angle that is used to measure the fluid velocity with a micrometer-size spatial resolution. Experimental results are in good agreement with theoretical calculations of optical and hydrodynamic torques on such a flag-shaped microsensor.

Synthesis and characterization of water-soluble two-photon excited blue fluorescent chromophores for bioimaging

We report here the synthesis and characterization of a new type of non-ionic blue fluorescent water-soluble chromophores specifically designed for two-photon absorption microscopy. The water solubility is induced by introduction of short oligo(ethylene glycol) monomethyl ether moieties. This work has led to low molecular weight dyes with efficient two-photon absorption cross sections and high fluorescence quantum yield in organic solvents as well as in aqueous solutions.

Photochromism of Spiropyran Nanocrystals Embedded in Sol−Gel Matrices

Spectroscopic and kinetic properties of a new photochromic medium, consisting of nanocrystals of spyropyran molecules (1,3-dihydro-1,3,3,5',6',pentamethyl-spiro[2H-indole-2,2'-[2H]pyrano [3,2-b]pyridinium] iodide) embedded in an organo-silicate sol-gel film, are presented and compared to microcrystals obtained by slow evaporation of a solvent. High photoconversion efficiencies for both kinds of crystals have been observed. In microcrystals, the photomerocyanine form absorbs at 570 nm with a fading rate of 5 h, in nanocrystals the photomerocyanine form absorbs at 535 nm with a fading rate of 41 h. Therefore, the crystalline structure of nanocrystals is different from the microcrystal one.

Synthesis, characterization and optical properties of π-conjugated systems incorporating closo-dodecaborate clusters: new potential candidates for two-photon absorption processes

Non-centrosymmetric pi-conjugated systems incorporating closo-dodecaborate clusters, [NC-C6H4-C(H=N(H)-B12H11]-(2), [NC-C6H4-C(H)=C(H)-C(6)H(4)-C(H)=N(H)-B12H11]-(3), and [NC-C6H4-C(H)=C(H)-C6H4-C(H)=C(H)-C6H4-C(H)=N(H)-B12H11]-(4) have been synthesized by reaction of the monoamino derivative of B12, [B12H11NH3]-(1), with various arylaldehydes, R-C6H4-CHO. These Schiff base-like compounds were fully characterized by multinuclear NMR spectroscopy and mass spectrometry. In order to evaluate these boron rich pi-systems as potential materials for two-photon absorption (TPA) processes, UV linear absorption curves were recorded for 3 and 4, and comparatively studied with those of the boron-free pi-systems NC-C6H4-C(H)=N-CH3(5) and NC-C6H4-C(H)=C(H)-C6H4-C(H)=N-CH3(6). The donor effect of the boron cluster was evidenced by a shift to the lower energy of the absorption band in the spectra of systems incorporating B12. The two photon absorption (TPA) spectrum of compound , obtained by the up-conversion method, shows a resonance at 720 nm with a cross-section sigma(TPA) of 35 x 10(-50) cm(4) s photon(-1) molecule(-1). This value suggests the potential of B12 clusters to be used as new donor groups for the synthesis of non-linear materials.

Three-dimensional microfabrication by two-photon-initiated polymerization with a low-cost microlaser

Fabrication of submicrometer structures by two-photon-initiated polymerization is performed with an inexpensive and low-power microlaser. This is made possible by the design of photoinitiators with strong two-photon absorption cross sections. We analyze the influence of both material properties and irradiation conditions on the two-photon polymerization rate and show that resins based on our highly sensitive two-photon photoinitiator can be solidified with microlaser excitation, whereas commercial UV photoresins require ultrashort and intense laser pulses.