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1.  Designing Two Self-Assembly Mechanisms into One Viral Capsid Protein 
Journal of the American Chemical Society  2012;134(45):18506-18509.
A structural fusion protein of the thermally-responsive elastin-like polypeptide and a viral capsid protein (ELP-CP) was designed and the assembly properties were investigated. Interestingly, this protein-based block copolymer could be self-assembled via two mechanisms into two different, well-defined nanocapsules: (1) pH-induced assembly yielded 28 nm virus-like particles and (2) ELP-induced assembly yielded 18 nm virus-like particles. The latter were a result of the emergent properties of the fusion protein. This work shows the feasibility to create a self-assembly system with new properties by combining two structural protein elements.
doi:10.1021/ja308132z
PMCID: PMC3510441  PMID: 23101937
2.  Multiplexed and Switchable Release of Distinct Fluids from Microneedle Platforms via Conducting Polymer Nanoactuators for Potential Drug Delivery 
Sensors and actuators. B, Chemical  2012;161(1):10.1016/j.snb.2011.11.085.
We report on the development of a microneedle-based multiplexed drug delivery actuator that enables the controlled delivery of multiple therapeutic agents. Two individually-addressable channels on a single microneedle array, each paired with its own reservoir and conducting polymer nanoactuator, are used to deliver various permutations of two unique chemical species. Upon application of suitable redox potentials to the selected actuator, the conducting polymer is able to undergo reversible volume changes, thereby serving to release a model chemical agent in a controlled fashion through the corresponding microneedle channels. Time-lapse videos offer direct visualization and characterization of the membrane switching capability and, along with calibration investigations, confirm the ability of the device to alternate the delivery of multiple reagents from individual microneedles of the array with higher precision and temporal resolution than conventional drug delivery actuators. Analytical modeling offers prediction of the volumetric flow rate through a single microneedle and accordingly can be used to assist in the design of subsequent microneedle arrays. The robust solid-state design and lack of mechanical components circumvent reliability issues that challenge fragile conventional microelectromechanical drug delivery devices. This proof-of-concept study demonstrates the potential of the drug delivery actuator system to aid in the rapid administration of multiple therapeutic agents and indicates the potential to counteract diverse biomedical conditions.
doi:10.1016/j.snb.2011.11.085
PMCID: PMC3809036  PMID: 24174709
Microneedle array; conducting polymer; electrochemically-switchable nanoactuator; drug delivery
3.  Differential assembly of Hepatitis B Virus core protein on single- and double-stranded nucleic acid suggest the dsDNA-filled core is spring-loaded 
Virology  2012;430(1):20-29.
Hepatitis B Virus (HBV) cores assemble on viral RNA, which is reverse transcribed within the core to the partially dsDNA genome of mature HBV. However, constraining dsDNA, a stiff polymer, within a core necessarily requires far greater capsid stability than constraining ssRNA. We hypothesized that, unlike ssRNA, dsDNA would be a poor substrate for assembly. We examined titrations of ssDNA and dsDNA with purified HBV core protein, Cp183, by EMSA, EM, DLS, and etheno-DNA fluorescence. Cp183 bound ssDNA with high affinity to form virus-like capsids. However, Cp183 bound dsDNA poorly, forming a mixture of irregular complexes. Nonetheless, we observed some normal cores in dsDNA assembly reactions, indicating that the energy required to bend DNA could be similar to the protein–protein association energy. This similarity of energies suggests that dsDNA stresses mature HBV cores, in agreement with calculation, which may be the basis for the virus maturation signal and DNA release.
doi:10.1016/j.virol.2012.04.012
PMCID: PMC3477361  PMID: 22595445
Hepadnavirus; Spumavirus; Capsid assembly; Self-assembly; Biophysics; RNA-binding; DNA-binding
4.  Rapid Antimicrobial Susceptibility Testing by Sensitive Detection of Precursor rRNA Using a Novel Electrochemical Biosensing Platform 
Precursor rRNA (pre-rRNA) is an intermediate stage in the formation of mature rRNA and is a useful marker for cellular metabolism and growth rate. We developed an electrochemical sensor assay for Escherichia coli pre-rRNA involving hybridization of capture and detector probes with tail sections that are spliced away during rRNA maturation. A ternary self-assembled monolayer (SAM) prepared on gold electrode surfaces by coassembly of thiolated capture probes with hexanedithiol and posttreatment with 6-mercapto-1-hexanol minimized the background signal and maximized the signal-to-noise ratio. Inclusion of internal calibration controls allowed accurate estimation of the pre-rRNA copy number per cell. As expected, the ratio of pre-rRNA to mature rRNA was low during stationary phase and high during log phase. Pre-rRNA levels were highly dynamic, ranging from 2 copies per cell during stationary phase to ∼1,200 copies per cell within 60 min of inoculation into fresh growth medium. Specificity of the assay for pre-rRNA was validated using rifampin and chloramphenicol, which are known inhibitors of pre-rRNA synthesis and processing, respectively. The DNA gyrase inhibitor, ciprofloxacin, was found to act similarly to rifampin; a decline in pre-rRNA was detectable within 15 min in ciprofloxacin-susceptible bacteria. Assays for pre-rRNA provide insight into cellular metabolism and are promising predictors of antibiotic susceptibility.
doi:10.1128/AAC.00615-12
PMCID: PMC3553690  PMID: 23229486
5.  Acoustic Droplet Vaporization and Propulsion of Perfluorocarbon-Loaded Microbullets for Targeted Tissue Penetration and Deformation 
Acoustic droplet vaporization of perfluorocarbon-loaded microbullets triggered by an ultrasound pulse provides the necessary force to penetrate, cleave, and deform cellular tissue for potential targeted drug delivery and precision nanosurgery.
doi:10.1002/anie.201201902
PMCID: PMC3477603  PMID: 22692791
microrocket/microbullet; acoustic droplet vaporization; perfluorinated solvents; electrostatic interactions; tissue penetration
6.  Electrochemical Sensing Based on Printable Temporary Transfer Tattoos† 
The realization of epidermal chemical sensing requires a fabrication methodology compatible with the non-planarity and irregularities of the human anatomy. This Communication describes the development of printed temporary transfer tattoo (T3) electrochemical sensors for physiological and security monitoring of chemical constituents leading towards the demonstration of ‘electronic skin’.
doi:10.1039/c2cc32839a
PMCID: PMC3387561  PMID: 22669136
7.  In Vitro Assembly of an Empty Picornavirus Capsid follows a Dodecahedral Path 
Journal of Virology  2012;86(23):13062-13069.
The Picornaviridae are a large family of small, spherical RNA viruses that includes numerous pathogens. The picornavirus structural proteins VP0, VP1, and VP3 are believed to first form protomers, which then form 14S particles and subsequently assemble to form empty and RNA-filled particles. 14S particles have long been presumed to be pentamers. However, the structure of the 14S particles, their mechanism of assembly, and the role of empty particles during infection are all unknown. We established an in vitro assembly system for bovine enterovirus (BEV) by using purified baculovirus-expressed proteins. By Rayleigh scattering, we determined that 14S particles are 488 kDa, confirming they are pentamers. Image reconstructions based on negative-stain electron microscopy showed that 14S particles have 5-fold symmetry, and their structures correlate extremely well with the corresponding pentamer from crystal structures of mature BEV. Purified 14S particles readily assemble in response to increasing ionic strength or temperature to form 5.8-MDa 12-pentamer particles, indistinguishable from native empty particles. Surprisingly, empty particles were sufficiently stable that, under physiological conditions, dissociation is unlikely to be a biologically relevant reaction. This suggests that empty particles are not a storage form of 14S particles, at least for bovine enterovirus, but are either a dead-end product or direct precursor into which viral RNA is packaged by as-yet-unidentified machinery.
doi:10.1128/JVI.01033-12
PMCID: PMC3497625  PMID: 23015694
8.  Multiplexed Microneedle-based Biosensor Array for Characterization of Metabolic Acidosis 
Talanta  2011;88:739-742.
The development of a microneedle-based biosensor array for multiplexed in situ detection of exercise-induced metabolic acidosis, tumor microenvironment, and other variations in tissue chemistry is described. Simultaneous and selective amperometric detection of pH, glucose, and lactate over a range of physiologically-relevant concentrations in complex media is demonstrated. Furthermore, materials modified with a cell-resistant (Lipidure®) coating were shown to inhibit macrophage adhesion; no signs of coating delamination were noted over a 48-hour period.
doi:10.1016/j.talanta.2011.11.046
PMCID: PMC3266534  PMID: 22265568
microneedle biosensor; microneedle; multiplexed detection; tumor microenvironment; carbon paste
9.  Bacterial Isolation by Lectin-Modified Microengines 
Nano Letters  2011;12(1):396-401.
New template-based self-propelled gold/nickel/polyaniline/platinum (Au/Ni/PANI/Pt) microtubular engines, functionalized with the Concanavalin A (ConA) lectin bioreceptor, are shown to be extremely useful for the rapid, real-time isolation of Escherichia coli (E. coli) bacteria from fuel-enhanced environmental, food and clinical samples. These multifunctional microtube engines combine the selective capture of E. coli with the uptake of polymeric drug-carrier particles to provide an attractive motion-based theranostics strategy. Triggered release of the captured bacteria is demonstrated by movement through a low-pH glycine-based dissociation solution. The smaller size of the new polymer-metal microengines offers convenient, direct and label-free optical visualization of the captured bacteria and discrimination against non-target cells.
doi:10.1021/nl203717q
PMCID: PMC3256279  PMID: 22136558
Nanomachines; microengines; lectin; E. coli isolation; theranostics; drug delivery; biodetection; complex samples
10.  Blood–spinal cord barrier pericyte reductions contribute to increased capillary permeability 
The blood–spinal cord barrier (BSCB) regulates molecular exchange between blood and spinal cord. Pericytes are presumed to be important cellular constituents of the BSCB. However, the regional abundance and vascular functions of spinal cord pericytes have yet to be determined. Utilizing wild-type mice, we show that spinal cord pericyte capillary coverage and number compared with the brain regions are reduced most prominently in the anterior horn. Regional pericyte variations are highly correlated with: (1) increased capillary permeability to 350 Da, 40,000 Da, and 150,000 Da, but not 2,000,000 Da fluorescent vascular tracers in cervical, thoracic, and lumbar regions and (2) diminished endothelial zonula occludens-1 (ZO-1) and occludin tight junction protein expression. Pericyte-deficient mutations (PdgfrβF7/F7 mice) resulted in additional pericyte reductions in spinal cord capillaries leading to overt BSCB disruption to serum proteins, accumulation in motor neurons of cyotoxic thrombin and fibrin and motor neuron loss. Barrier disruption in perciyte-deficient mice coincided with further reductions in ZO-1 and occludin. These data suggest that pericytes contribute to proper function of the BSCB at the capillary level. Regional reductions in spinal cord pericytes may provide a cellular basis for heightened spinal cord barrier capillary permeability and motor neuron loss.
doi:10.1038/jcbfm.2012.113
PMCID: PMC3463878  PMID: 22850407
blood–brain barrier; capillaries; endothelium; pericytes; vascular biology
11.  Structural Organization of Pregenomic RNA and the Carboxy-Terminal Domain of the Capsid Protein of Hepatitis B Virus 
PLoS Pathogens  2012;8(9):e1002919.
The Hepatitis B Virus (HBV) double-stranded DNA genome is reverse transcribed from its RNA pregenome (pgRNA) within the virus core (or capsid). Phosphorylation of the arginine-rich carboxy-terminal domain (CTD) of the HBV capsid protein (Cp183) is essential for pgRNA encapsidation and reverse transcription. However, the structure of the CTD remains poorly defined. Here we report sub-nanometer resolution cryo-EM structures of in vitro assembled empty and pgRNA-filled Cp183 capsids in unphosphorylated and phosphorylation-mimic states. In empty capsids, we found unexpected evidence of surface accessible CTD density partially occluding pores in the capsid surface. We also observed that CTD organization changed substantively as a function of phosphorylation. In RNA-filled capsids, unphosphorylated CTDs favored thick ropes of RNA, while the phosphorylation-mimic favored a mesh of thin, high-density strands suggestive of single stranded RNA. These results demonstrate that the CTD can regulate nucleic acid structure, supporting the hypothesis that the HBV capsid has a functional role as a nucleic acid chaperone.
Author Summary
Many single stranded RNA virus encapsidate their genome through positively-charged domains of their capsid proteins. Hepatitis B virus (HBV) is a double stranded DNA virus which packages a single-stranded RNA pregenome (pgRNA) that is reverse transcribed within the capsid. RNA packaging requires a phosphorylated form of the HBV capsid protein's RNA-binding carboxy-terminal domain (CTD). Although the capsid has been well studied, the internal structures, the CTDs and the packaged RNA, are poorly characterized. By using in vitro reassembly, we have generated empty and pgRNA-filled capsids using phosphorylation-mimic and unphosphorylated forms of the capsid protein. Using cryo-EM image reconstruction, we have been able to show the structure of encapsidated pgRNA and, independently, the CTD in the absence of RNA to visualize early stages of the HBV assembly. We showed that the structural organization of the CTD changes as a function of the phosphorylation. Changes in CTD structure affect the structure of the encapsidated pgRNA, changing it from thin segments of density in the phosphorylated state, suggestive of single-stranded RNA, to thick rope-like structures consistent with duplex nucleic acid in the unphosphorylated state.
doi:10.1371/journal.ppat.1002919
PMCID: PMC3447754  PMID: 23028319
12.  Quantitative measures detect sensory and motor impairments in multiple sclerosis 
Journal of the neurological sciences  2011;305(1-2):103-111.
Background
Sensory and motor dysfunction in multiple sclerosis (MS) is often assessed with rating scales which rely heavily on clinical judgment. Quantitative devices may be more precise than rating scales.
Objective
To quantify lower extremity sensorimotor measures in individuals with MS, evaluate the extent to which they can detect functional systems impairments, and determine their relationship to global disability measures.
Methods
We tested 145 MS subjects and 58 controls. Vibration thresholds were quantified using a Vibratron-II device. Strength was quantified by a hand-held dynamometer. We also recorded Expanded Disability Status Scale (EDSS) and timed 25-foot walk (T25FW). T-tests and Wilcoxon-rank sum were used to compare group data. Spearman correlations were used to assess relationships between each measure. We also used a step-wise linear regression model to determine how much the quantitative measures explain the variance in the respective functional systems scores (FSS).
Results
EDSS scores ranged from 0-7.5, mean disease duration was 10.4±9.6 years, and 66% were female. In RRMS, but not progressive MS, poorer vibration sensation correlated with a worse EDSS score, whereas progressive groups’ ankle/hip strength changed significantly with EDSS progression. Interestingly, not only did sensorimotor measures significantly correlate with global disability measures (EDSS), but they had improved sensitivity, as they detected impairments in up to 32% of MS subjects with normal sensory FSS.
Conclusions
Sensory and motor deficits can be quantified using clinically accessible tools and distinguish differences among MS subtypes. We show that quantitative sensorimotor measures are more sensitive than FSS from the EDSS. These tools have the potential to be used as clinical outcome measures in practice and for future MS clinical trials of neurorehabilitative and neuroreparative interventions.
doi:10.1016/j.jns.2011.03.003
PMCID: PMC3090542  PMID: 21458828
multiple sclerosis; demyelinating disease; outcome measures; neurological disability; rehabilitation
14.  Ternary Monolayers as DNA Recognition Interfaces for Direct and Sensitive Electrochemical Detection in Untreated Clinical Samples 
Biosensors & bioelectronics  2011;26(8):3577-3583.
Detection of specific DNA sequences in clinical samples is a key goal of studies on DNA biosensors and gene chips. Herein we present a highly sensitive electrochemical genosensor for direct measurements of specific DNA sequences in undiluted and untreated human serum and urine samples. Such genosensing relies on a new ternary interface involving hexanedithiol (HDT) co-immobilized with the thiolated capture probe (SHCP) on gold surfaces, followed by the incorporation of 6-mercapto-1-hexanol (MCH) as diluent. The performance of ternary monolayers prepared with linear dithiols of different lengths was systematically examined, compared and characterized by cyclic voltammetry and electrochemical impedance spectroscopy, with HDT exhibiting the most favorable analytical performance. The new SHCP/HDT+MCH monolayer led to a 80-fold improvement in the signal-to-noise ratio (S/N) for 1 nM target DNA in undiluted human serum over the common SHCP/MCH binary alkanethiol interface, and allowed the direct quantification of the target DNA down to 7 pM (28 amol) and 17 pM (68 amol) in undiluted/untreated serum and urine, respectively. It also displayed attractive antifouling properties, as indicated from the favorable S/N obtained after a prolonged exposure (24 h) to untreated biological matrices. These attractive features of the SHCP/HDT+MCH sensor interface indicate considerable promise for a wide range of clinical applications.
doi:10.1016/j.bios.2011.02.004
PMCID: PMC3065524  PMID: 21377347
Dithiols; self-assembled monolayer; clinical samples; electrochemical detection; hybridization; DNA
15.  Development of Amperometric α-Ketoglutarate Biosensor based on Ruthenium-Rhodium Modified Carbon Fiber Enzyme Microelectrode 
Biosensors & bioelectronics  2011;26(8):3670-3673.
A rapid and highly sensitive miniaturized amperometric biosensor for the detection α-ketoglutarate (α-KG) based on a carbon fiber electrode (CFE) is presented. The biosensor is constructed by immobilizing the enzyme, glutamate dehydrogenase (GLUD) on the surface of single carbon fiber modified by co-deposition of ruthenium (Ru) and rhodium (Rh) nanoparticles. SEM and EDX shed useful insights into the morphology and composition of the modified microelectrode. The mixed Ru/Rh coating offers a greatly enhanced electrocatalytic activity towards the detection of β-nicotinamide adenine dinucleotide (NADH), with a substantial decrease in overpotential of ~400 mV compared to the unmodified CFE. It also imparts higher stability with minimal surface fouling, common to NADH oxidation. Further modification with the enzyme, GLUD leads to effective amperometric biosensing of α-KG through monitoring of the NADH consumption. A very rapid response to dynamic changes in the α-KG concentrations is observed with a response time of 6s. The current response is linear between 100 and 600 μM with a sensitivity of 42 μA M−1 and a detection limit of 20 μM. This proof of concept study indicates that the GLUD-Ru/Rh-CFE biosensor holds great promise for real-time electrochemical measurements of α-KG.
doi:10.1016/j.bios.2011.01.026
PMCID: PMC3065949  PMID: 21334188
Amperometric biosensor; α-Ketoglutarate; NADH; Ru; Rh; Carbon fiber electrode
16.  Ternary Surface Monolayers for Ultrasensitive (Zeptomole) Amperometric Detection of Nucleic-Acid Hybridization without Signal Amplification 
Analytical chemistry  2010;82(21):10.1021/ac101474k.
A ternary surface monolayer, consisting of co-assembled thiolated capture probe (SHCP) mercaptohexanol (MCH) and dithiothreitol (DTT), is shown to offer dramatic improvements in the signal-to-noise characteristics of electrochemical DNA hybridization biosensors based on common self-assembled monolayers (SAMs). Remarkably low detection limits down to 40 zmole (in 4 μL samples) as well as only 1 CFU E. coli per sensor are thus obtained without any additional amplification step in connection to the commonly used horseradish peroxidase/3,3′,5,5′-tetramethylbenzidine (HRP/TMB) system. Such dramatic improvements in the detection limits (compared to common binary alkanethiol interfaces and to most electrochemical DNA sensing strategies without target or signal amplification) are attributed primarily to the remarkably higher resistance to non-specific adsorption. This reflects the highly compact layer (with lower pinhole density) produced by the coupling of the cyclic- and linear-configuration ‘backfillers’ that leads to a remarkably low background noise even in the presence of complex sample matrices. A wide range of surface compositions have been investigated and the ternary mixed monolayer has been systematically optimized. Detailed impedance spectroscopy and cyclic voltammetric studies shed useful insights into the surface coverage. The impressive sensitivity and high specificity of the simple developed methodology indicate great promise for a wide range of nucleic acid testing, including clinical diagnostics, biothreat detection, food safety and forensic analysis.
doi:10.1021/ac101474k
PMCID: PMC3038188  PMID: 20883023
17.  Redox cycling amplified electrochemical detection of DNA hybridization: Application to pathogen E. coli bacterial RNA 
Analytica chimica acta  2011;689(1):29-33.
An electrochemical genosensor in which signal amplification is achieved using p-aminophenol (p-AP) redox cycling by nicotinamide adenine dinucleotide (NADH) is presented. An immobilized thiolated capture probe is combined with a sandwich-type hybridization assay, using biotin as a tracer in the detection probe, and streptavidin-alkaline phosphatase as reporter enzyme. The phosphatase liberates the electrochemical mediator p-AP from its electrically inactive phosphate derivative. This generated p-AP is electrooxidized at an Au electrode modified self-assembled monolayer to p-quinone imine (p-QI). In the presence of NADH, p-QI is reduced back to p-AP, which can be re-oxidized on the electrode and produce amplified signal. A detection limit of 1 pM DNA target is offered by this simple one-electrode, one-enzyme format redox cycling strategy. The redox cycling design is applied successfully to the monitoring of the 16S rRNA of E. coli pathogenic bacteria, and provides a detection limit of 250 CFU μL−1.
doi:10.1016/j.aca.2011.01.014
PMCID: PMC3053385  PMID: 21338752
Electrochemistry; Genosensor; Amplification; Redox cycling; Escherichia coli
18.  A Kinase Chaperones Hepatitis B Virus Capsid Assembly and Captures Capsid Dynamics in vitro 
PLoS Pathogens  2011;7(11):e1002388.
The C-terminal domain (CTD) of Hepatitis B virus (HBV) core protein is involved in regulating multiple stages of the HBV lifecycle. CTD phosphorylation correlates with pregenomic-RNA encapsidation during capsid assembly, reverse transcription, and viral transport, although the mechanisms remain unknown. In vitro, purified HBV core protein (Cp183) binds any RNA and assembles aggressively, independent of phosphorylation, to form empty and RNA-filled capsids. We hypothesize that there must be a chaperone that binds the CTD to prevent self-assembly and nonspecific RNA packaging. Here, we show that HBV capsid assembly is stalled by the Serine Arginine protein kinase (SRPK) binding to the CTD, and reactivated by subsequent phosphorylation. Using the SRPK to probe capsids, solution and structural studies showed that SRPK bound to capsid, though the CTD is sequestered on the capsid interior. This result indicates transient CTD externalization and suggests that capsid dynamics could be crucial for directing HBV intracellular trafficking. Our studies illustrate the stochastic nature of virus capsids and demonstrate the appropriation of a host protein by a virus for a non-canonical function.
Author Summary
A virus particle is a molecular machine that has evolved to self-assemble within the confines of a living cell. For hepatitis B virus (HBV), outside of a cell, the self-assembly process is very aggressive and consequently not specific for viral RNA. Here we show that HBV takes advantage of a host protein, SRPK, which acts like a molecular chaperone, to prevent the HBV core protein from binding RNA and to prevent the core protein from assembling at the wrong time and place. At the right time, SRPK can be removed in a regulated reaction to allow assembly. Once a virus is assembled, it must traffic to the right intracellular locale. Using SRPK, we show that HBV cores can transiently expose a segment of protein, normally inside the virus, that carries a signal for transport to the host nucleus. This is the first example we know of where a virus repurposes an enzyme for an alternative function. This sort of interplay between virus and host, where the virus hijacks and repurposes host proteins, is likely to be a common feature of viral infection.
doi:10.1371/journal.ppat.1002388
PMCID: PMC3219723  PMID: 22114561
19.  Ultrasensitive aptamer-based protein detection via a dual amplified biocatalytic strategy 
Biosensors & bioelectronics  2010;25(11):2539-2542.
We present an ultrasensitive aptasensor for electronic monitoring of proteins through a dual amplified strategy in this paper. The target protein thrombin is sandwiched between an electrode surface confined aptamer and an aptamer-enzyme-carbon nanotube bioconjugate. The analytical signal amplification is achieved by coupling the signal amplification nature of multiple enzymes with the biocatalytic signal enhancement of redox-recycling. Our novel dramatic signal amplification strategy, with a detection limit of 8.3 fM, shows about 4 orders of magnitude improvement in sensitivity for thrombin detection compared to other universal single enzyme-based assay. This makes our approach an attractive alternative to other common PCR-based signal amplification in ultralow level of protein detection.
doi:10.1016/j.bios.2010.04.007
PMCID: PMC2878878  PMID: 20452761
amplification; aptamers; bi-enzyme; biosensors; proteins; ultrasensitive detection
20.  Spatial Configuration of Hepatitis E Virus Antigenic Domain ▿  
Journal of Virology  2010;85(2):1117-1124.
Hepatitis E virus (HEV) is a human pathogen that causes acute hepatitis. When an HEV capsid protein containing a 52-amino-acid deletion at the C terminus and a 111-amino-acid deletion at the N terminus is expressed in insect cells, the recombinant HEV capsid protein can self-assemble into a T=1 virus-like particle (VLP) that retains the antigenicity of the native HEV virion. In this study, we used cryoelectron microscopy and image reconstruction to show that anti-HEV monoclonal antibodies bind to the protruding domain of the capsid protein at the lateral side of the spikes. Molecular docking of the HEV VLP crystal structure revealed that Fab224 covered three surface loops of the recombinant truncated second open reading frame (ORF2) protein (PORF2) at the top part of the spike. We also determined the structure of a chimeric HEV VLP and located the inserted B-cell tag, an epitope of 11 amino acids coupled to the C-terminal end of the recombinant ORF2 protein. The binding site of Fab224 appeared to be distinct from the location of the inserted B-cell tag, suggesting that the chimeric VLP could elicit immunity against both HEV and an inserted foreign epitope. Therefore, the T=1 HEV VLP is a novel delivery system for displaying foreign epitopes at the VLP surface in order to induce antibodies against both HEV and the inserted epitope.
doi:10.1128/JVI.00657-10
PMCID: PMC3020005  PMID: 21068233
21.  Reverse-Micelle Synthesis of Electrochemically Encoded Quantum Dot Barcodes: Application to Electronic Coding of a Cancer Marker 
Analytical chemistry  2010;82(3):1138-1141.
Reproducible electrochemically encoded quantum dot (QD) barcodes were prepared by using the reverse-micelle synthetic approach. The encoding elements, Zn2+, Cd2+, Pb2+ were confined within a single QD, which eliminates the cumbersome encapsulation process used by other common nanoparticle-based barcode preparation schemes. The distinct voltammetric stripping patterns of Zn2+, Cd2+, Pb2+ at distinguishable potentials with controllable current intensities offer excellent encoding capability for the prepared electrochemical (EC) QDs. Additionally, the simultaneous modification of the QD barcode surface with organic ligands during the preparation process make them potentially useful in biomedical research. For proof of concept of their application in bioassays, the EC QD barcodes were further employed as tags for an immunoassay of a cancer marker, carcinoembryonic antigen (CEA). The voltammetric stripping response of the dissolved bardcode tags was proportional to log[CEA] in the range from 0.01 ng mL−1 to 80 ng mL−1, with a detection limit of 3.3 pg mL−1. The synthesized EC QD barcodes hold considerable potentials in biodetection, encrypted information and product tracking.
doi:10.1021/ac902335e
PMCID: PMC2836120  PMID: 20067269
22.  Potentiometric Detection of DNA Hybridization using Enzyme-Induced Metallization and a Silver Ion Selective Electrode 
Analytical chemistry  2009;81(24):10007-10012.
Here we report on a highly sensitive potentiometric detection of DNA hybridization. The new assay uses a low-volume solid-contact silver ion-selective electrode (Ag+-ISE) to monitor the depletion of silver ions induced by the biocatalytic reaction of the alkaline-phosphatase enzyme tag. The resultant potential change of the Ag+-ISE thus serves as the hybridization signal. Factors affecting the potentiometric hybridization response have been optimized to offer a detection limit of 50 fM (0.2 amol) DNA target. The new potentiometric assay was applied successfully to the monitoring of the 16S rRNA of E. coli pathogenic bacteria to achieve a low detection limit of 10 CFU in the 4 μL sample. Such potentiometric transduction of biocatalytically-induced metallization processess holds great promise for monitoring various bioaffinity assays involving common enzyme tags.
doi:10.1021/ac9018507
PMCID: PMC2794934  PMID: 19908886
23.  High Temperature Potentiometry: Modulated Response of Ion-Selective Electrodes During Heat Pulses 
Analytical chemistry  2009;81(24):10290-10294.
The concept of locally heated polymeric membrane potentiometric sensors is introduced here for the first time. This is accomplished in an all solid state sensor configuration, utilizing poly(3-octylthiophene) as intermediate layer between the ion-selective membrane and underlying substrate that integrates the heating circuitry. Temperature pulse potentiometry (TPP) gives convenient peak-shaped analytical signals and affords an additional dimension with these sensors. Numerous advances are envisioned that will benefit the field. The heating step is shown to give an increase in the slope of the copper-selective electrode from 31 mV to 43 mV per 10-fold activity change, with a reproducibility of the heated potential pulses of 1% at 10 µM copper levels and a potential drift of 0.2 mV/h. Importantly, the magnitude of the potential pulse upon heating the electrode changes as a function of the copper activity, suggesting an attractive way for differential measurement of these devices. The heat pulse is also shown to decrease the detection limit by half an order of magnitude.
doi:10.1021/ac902191h
PMCID: PMC2827483  PMID: 19928777
Potentiometry; Heated electrodes; Ion-selective electrodes; Temperature pulse
24.  Effects of Heterogeneous Electron-Transfer Rate on the Resolution of Electrophoretic Separations based on Microfluidics with End-Column Electrochemical Detection 
Electrophoresis  2009;30(19):3334-3338.
We demonstrate here that the electrode kinetics of an electrochemical detector contributes greatly to the resolution of the analyte bands in microchip electrophoresis systems with amperometric detection. The separation performance in terms of resolution and theoretical plate number can be improved and tailored by selecting or modifying the working electrode and/or by controlling the detection potential. Such improvements in the separation performance reflect the influence of the heterogeneous electron transfer rate of electroactive analytes upon the post-channel band broadening, as illustrated for catechol and hydrazine compounds. The electrode kinetics thus has a profound effect not only upon the sensitivity of electrochemical detectors but upon the separation efficiency and the overall performance of microchip-electrochemistry systems.
doi:10.1002/elps.200800845
PMCID: PMC2994016  PMID: 19728304
electron transfer; resolution; surface modification; amperometry; microfluidics
25.  REAL-TIME PROBING OF THE GROWTH DYNAMICS OF NANOPARTICLES USING POTENTIOMETRIC ION-SELECTIVE ELECTRODES 
Electrochemistry communications  2009;11(10):1964-1967.
This Communication demonstrates the ability of potentiometric ion-selective electrodes (ISE) to probe the growth dynamics of metal nanoparticles in real-time. The new monitoring capability is illustrated using a solid-contact silver ISE for monitoring the hydroquinone-induced precipitation of silver on gold nanoparticle seeds. Potential-time recordings obtained under different conditions are used to monitor the depletion of the silver ion during the nanoparticle formation and shed useful insights into the growth dynamics of the nanoparticles. Such potentiometric profiles correlate well with the analogous optical measurements. The new real-time electrochemical probing of the particle growth process reflects the direct, rapid and sensitive response of modern ISE to changes in the level of the precipitated metal ion from the bulk solution and holds considerable promise for probing the preparation of different nanoscale materials.
doi:10.1016/j.elecom.2009.08.029
PMCID: PMC2777707  PMID: 20161363
Nanoparticles; Growth; Ion-selective electrodes; Potentiometry; Silver; Hydroquinone

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