Single molecule immunoassay on plasmonic platforms

We examined the photophysical properties of the new near infrared (NIR) fluorescent label SeTau-665 on a plasmonic platform of self- assembled colloidal structures (SACS) of silver prepared on a semitransparent silver film. A SeTau-665 immunoassay was performed on this platform and a control glass slide. The fluorescence properties of this label substantially change due to plasmonic interactions. While the average brightness increase of SeTau 665 in ensemble measurements was about 70-fold, fluorescence enhancements up to four-hundred times were observed on certain "hot spots" for single molecule measurements. The intensity increase is strongly correlated with a simultaneous decrease in fluorescence lifetime in these "hot spots". The large increase in brightness allows the reduction of the excitation power resulting in a reduced background and increased photostability. The remarkable fluorescence enhancements observed for SeTau 665 on our plasmonic platform should allow to substantially improve single molecule detection and to reduce the detection limits in sensing devices.

Minimization of detection volume by surface-plasmon-coupled emission

We report theoretical predictions and experimental observations of the reduced detection volume with the use of surface-plasmon-coupled emission (SPCE). The effective fluorescence volume (detection volume) in SPCE experiments depends on two near-field factors: the depth of evanescent wave excitation and a distance-dependent coupling of excited fluorophores to the surface plasmons. With direct excitation of the sample (reverse Kretschmann excitation) the detection volume is restricted only by the distance-dependent coupling of the excitation to the surface plasmons. However, with the excitation through the glass prism at surface plasmon resonance angle (Kretschmann configuration), the detection volume is a product of evanescent wave penetration depth and distance-dependent coupling. In addition, the detection volume is further reduced by a metal quenching of excited fluorophores at a close proximity (below 10nm). The height of the detected volume size is 40-70nm, depending on the orientation of the excited dipoles. We show that, by using the Kretschmann configuration in a microscope with a high-numerical-aperture objective (1.45) together with confocal detection, the detection volume can be reduced to 1-2attoL. The strong dependence of the coupling to the surface plasmons on the orientation of excited dipoles can be used to study the small conformational changes of macromolecules.

[Synthesis of phthalocyanine conjugates with monoclonal antibodies in AOT/n-octane reversed micelles and in water-organic solvent mixtures]

Conjugates of cobalt and aluminum phthalocyanines with monoclonal antibodies were synthesized using an AOT/n-octane reversed micellar system or water-organic mixtures with a low content of organic solvent as media. The effect of the degree of hydration of the micelles and the concentration of phthalocyanines on the composition of conjugates was studied. The immune activity of the resulting conjugates in comparison to that of native antibodies was evaluated. The catalytic activity of free cobalt phthalocyanines and their antibody conjugates was studied in the reaction of ascorbic acid oxidation.

[Polarization fluoroimmunoassay of propazine in reversed micelles of aerosol OT in octane]

The interaction between fluorescein-labeled propazine and antibodies against this hapten was studied in the reversed micelles of Aerosol OT in n-octane by a polarization fluoroassay. The effect of the hydration degree of micelles W0 (W0=[H2O]/[Surf]), which determines their size and surfactant concentration, on the binding of the antigen with antibodies was studied. A high hydration degree of the reversed micelles (W0 = 15-30) and low concentration of the surfactant (less than 50 microM) are optimal for binding. The binding efficacy depends upon the structure of the fluorescein-labeled hapten, particularly upon the length of the bridge binding fluorescein with propazine. It was shown that the polarization fluoroimmunoassay of propazine may be carried out in a reversed micellar system in nonpolar organic solvent (octane) with a detection limit of about 100 nM (20 microns/l). This is an order of magnitude higher than that achievable upon analysis in aqueous medium. The proposed polarization fluoroimmunoassay in a reversed micellar system makes it possible to detect haptens that are poorly soluble in water directly in organic extracts, e.g. in chloroform solutions.

Antigen--antibody interactions in the reverse micellar system: quenching of the fluorescence of fluorescein-labeled atrazine by antibodies against atrazine

This work presents a new method for performing homogeneous fluoroimmunoassay in apolar organic media, quenching fluoroimmunoassay (QFIA). This method is based on utilization of the reverse micellar system of Aerosol OT (AOT) in n-octane as a medium for the analysis of compounds with low water solubility. It is shown using the system for determination of a hydrophobic pesticide atrazine as an example. The conjugate of atrazine with fluorescein (FA) serves as a label for fluorescence detection of antigen-antibody interaction in the reverse micellar system. The fluorescence quantum yield of this compound drastically depends on the micro-environment of the label in the reverse micelle system. Specifically, the binding of this conjugate with the antibodies solubilized in the reverse micelles results in fluorescence quenching. We found that quenching efficiency depends on the properties of the reverse micellar system (surfactant concentration, hydration degree w0, w0 = [water]/[surfactant], etc.). The optimal conditions for quenching of FA fluorescence by antibodies in reverse micelles of AOT in n-octane are low surfactant concentration and hydration degree, allowing one to get large reversed micelles (w0 = 15-20) capable of retaining solubilized antibodies. Addition of free atrazine results in displacement of the conjugate and restoration of its fluorescence. The sensitivity of the analysis to atrazine is only 10 times less than that of the commonly used method of homogeneous immunoassay, polarization fluoroimmunoassay, in aqueous solution using the same antibodies and conjugate. The advantage of QFIA in reverse micelles is that the analyte can be added when dissolved in nonpolar organic solvent.

[Orthopedic devices for footwear in flatness of the anterior part of the foot]

The work is dedicated to the problem of orthopedic supply of patients with flatness of the anterior part of foot. There is proposed a number of footwear orthopedic devices made of foam rubber. There is described the technology of their production with application of modern polymeric materials. There has been studied prosthetics of 50 patients with flatness of foot and revealed the positive result of application of footwear orthopedic devices made of foam rubber.

[Relaxation phenomena in systems of protein-containing reverse micelles of surfactants in organic solvents]

The research was aimed to establish the equilibrium processes in protein-containing systems of AOT reverse micelles in octane. As chromophore label for tracing the kinetics of the process, the acid-base indicator, p-nitrophenol, was used. The establishing of the equilibrium in the reverse micelle system notably decelerated in the presence of a solubilized protein (native and stearoylated alpha-chymotrypsin). During the establishing of the equilibrium, the solubilized enzyme can be irreversibly inactivated. The level of the residual activity of the enzyme in the equilibrium system depended on the procedure of micellar system preparation. The methods have been offered to set up the equilibrium in the reverse micelle system without inactivation of the solubilized enzyme.