Evgueni E. Nesterov

Smart optical probes for near-infrared fluorescence imaging of Alzheimer's disease pathology.

PurposeNear-infrared fluorescent probes for amyloid-beta (Aβ) are an exciting option for molecular imaging in Alzheimer’s disease research and may translate to clinical diagnostics. However, Aβ-targeted optical probes often suffer from poor specificity and slow clearance from the brain. We are designing smart optical probes that emit characteristic fluorescence signal only when bound to Aβ.MethodsWe synthesized a family of dyes and tested Aβ-binding sensitivity with fluorescence spectroscopy and tissue-staining.ResultsSelect compounds exhibited Aβ-dependent changes in fluorescence quantum yield, lifetime, and emission spectra that may be imaged microscopically or in vivo using new lifetime and spectral fluorescence imaging techniques.ConclusionSmart optical probes that turn on when bound to Aβ will improve amyloid detection and may enable quantitative molecular imaging in vivo.

Near-Infrared Fluorophores Containing Benzo[c]heterocycle Subunits

The syntheses and spectroscopic properties of eight new push-pull-type near-infrared fluorophores that contain either isobenzofuran or isothianaphthene subunits are presented. The isobenzofuran dyes demonstrate significantly red-shifted absorption compared with their isothianaphthene counterparts, which is attributed to isobenzofurans more potent pro-quinoidal character.

Rational Design of Highly Responsive pH Sensors Based on DNA i-Motif

Availability of strategies for molecular biosensing over a finely adjustable dynamic range is essential for understanding and controlling vital biological processes. Herein we report design principles of highly responsive pH sensors based on a DNA i-motif where both response sensitivity and transition midpoint can be tuned with high precision over the physiologically relevant pH interval. The tuning is accomplished via rational manipulations of an i-motif structure as well as incorporation of allosteric control elements. This strategy delivers molecular sensing systems with a transition midpoint tunable with 0.1 pH units precision and with a total response range as narrow as 0.2 pH units which can be adjusted to a variety of outputs (e.g., fluorescent readout). The potential of the presented approach is not limited by pH sensing but may extend toward manipulation of other quadruplex based structures or the development of ultraresponsive elements for artificial molecular machines and signaling systems.

Detection of Myelination Using a Novel Histological Probe

Current methods for myelin staining in tissue sections include both histological and immunohistochemical techniques. Fluorescence immunohistochemistry, which uses antibodies against myelin components such as myelin basic protein, is often used because of the convenience for multiple labeling. To facilitate studies on myelin, this paper describes a quick and easy method for direct myelin staining in rodent and human tissues using novel near-infrared myelin (NIM) dyes that are comparable to other well-characterized histochemical reagents. The near-infrared fluorescence spectra of these probes allow fluorescent staining of tissue sections in multiple channels using visible light fluorophores commonly used in immunocytochemistry. These dyes have been used successfully to detect normal myelin structure and myelin loss in a mouse model of demyelination disease.

Self-Assembled Monolayer Initiated Electropolymerization: A Route to Thin-Film Materials with Enhanced Photovoltaic Performance

Continuing progress in the field of organic polymer photovoltaic (PV) devices requires the development of new materials with better charge-transport efficiency. To improve this parameter, we have investigated surface-attached bilayer polymer PV thin films prepared starting from a covalently attached monolayer of an electroactive initiator using sequential electropolymerization of dithiophene and its derivatives. These systems were found to show significantly increased photocurrent generation quantum yields as compared to systems made through conventional approaches. In addition, the described PV thin films possess remarkable mechanical, air, and photostability. These properties likely arise from the more uniform and better ordered bulk layer morphologies as well as tighter covalently bonded contacts at the interfacial junctions, contributing to improved charge transport. While more studies on the fundamental reasons behind the discovered phenomenon are currently underway, this information can be readily applied to build more efficient organic polymer photovoltaics.

Energy migration in conjugated polymers: the role of molecular structure

Conjugated polymers undergo facile exciton diffusion. Different molecular structures were examined to study the role of the excited state lifetimes and molecular conformations on energy transfer. There is a clear indication that extended fluorescence lifetimes give enhanced exciton diffusion as determined by fluorescence depolarization measurements. These results are consistent with a strong electronic coupling or Dexter-type energy transfer as the dominating mechanism. The control of polymer conformations in liquid crystal solvents was also examined and it was determined that more planar conformations gave enhanced energy transfer to emissive low band-gap endgroups.

Long-Chain 3,4-Ethylenedioxythiophene/Thiophene Oligomers and Semiconducting Thin Films Prepared by Their Electropolymerization

A series of soluble H-terminated conjugated oligomers incorporating 3,4-ethylenedioxythiophene (EDOT) combined with a small number of thiophene units and ranging in length from four to eight EDOT/thiophene groups was prepared with the ultimate goal to investigate if facile formation of a reactive trication radical species would enable electrochemical polymerization of such long-chain oligomers. Spectroscopic and electrochemical studies of the oligomers revealed some general dependencies of their electronic properties on the total number and position of EDOT groups. It was the number of consecutive EDOT units rather than total number of these units which was found to have the most profound effect on electronic energy gap and conjugation length. This influence originates from the especially strong planarization induced in the conjugated backbone by the incorporation of EDOT units. In contrast, incorporation of thiophene units was found to result in loss of the conformational stabilization. This phenomenon was analyzed using the natural bond orbital computational approach, which revealed the predominantly hyperconjugative nature of the EDOT-induced conformational stabilization. Whereas shorter oligomers, in agreement with the general consensus, were found to be inert toward electrochemical polymerization due to low reactivity of electrochemically generated cation radical and dication species, the longest oligomer showed an unprecedentedly efficient electropolymerization to yield a stable thin film of an electroactive polymer. The efficient electropolymerization of the long-chain oligomer was found to be in agreement with the formation of a reactive trication radical species. The electronic and spectral properties of the resulting semiconducting polymer film were studied by various electrochemical and spectroelectrochemical methods, as well as conductive probe AFM technique, and revealed a number of unusual features (such as electrical rectifying switching behavior) consistent with the possibility of increased molecular order in this material.

Development and screening of contrast agents for in vivo imaging of Parkinson's disease.

PurposeThe goal was to identify molecular imaging probes that would enter the brain, selectively bind to Parkinson’s disease (PD) pathology, and be detectable with one or more imaging modalities.ProcedureA library of organic compounds was screened for the ability to bind hallmark pathology in human Parkinson’s and Alzheimer’s disease tissue, alpha-synuclein oligomers and inclusions in two cell culture models, and alpha-synuclein aggregates in cortical neurons of a transgenic mouse model. Finally, compounds were tested for blood–brain barrier permeability using intravital microscopy.ResultsSeveral lead compounds were identified that bound the human PD pathology, and some showed selectivity over Alzheimer’s pathology. The cell culture models and transgenic mouse models that exhibit alpha-synuclein aggregation did not prove predictive for ligand binding. The compounds had favorable physicochemical properties, and several were brain permeable.ConclusionsFuture experiments will focus on more extensive evaluation of the lead compounds as PET ligands for clinical imaging of PD pathology.

Design and evaluation of an i-motif-based allosteric control mechanism in DNA-hairpin molecular devices.

Molecular devices designed to assess and manipulate biologically relevant conditions with required accuracy and precision play an essential role in life sciences research. Incorporating allosteric regulation mechanism is an attractive strategy toward more efficient artificial sensing and switching systems. Herein, we report on a new principle of regulating switching parameters of a DNA-based molecular device based on allosteric interaction between spatially separated hairpin stem and a tetraplexed fragment (i.e., i-motif). We characterized thermodynamic and kinetic effects arising from interaction between functional domains of the device and demonstrated the potential of applying the allosteric control principle for rational design of sensors and switches with precisely defined operational characteristics.

Surface‐Immobilized Monolayers of Conjugated Oligomers as a Platform for Fluorescent Sensors Design: The Effect of Exciton Delocalization on Chemosensing Performance

Surface-immobilized monolayers of fluorescent molecular sensors consisting of a short conjugated oligo(p-phenylene ethynylene) core end-capped with an acceptor fluorophore (analyte receptor) display significant signal amplification due to enhanced intermolecular energy transfer within the monolayer. This general phenomenon offers a superior platform for designing ratiometric fluorescent sensors. An example of how this can be used to convert a narrow-range threshold fluorescent pH indicator (fluorescein) to a broad-range ratiometric fluorescent chemosensor is described.