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Biomedical subjects

Hai-Feng Ji

Publications and source records attributed to Hai-Feng Ji.

18 recordsLinked to original sources
PubMed2006

Surface stress changes induced by the conformational change of proteins.

A potential binding assay based on conformational-change-induced micromechanical motion is described. Calmodulin was used to modify a microcantilever (MCL) by a self-assembled layer-by-layer approach. The results showed that the modified MCL bent when the proteins changed their conformation upon binding with Ca2+. The cantilever deflection amplitudes were different under different ionic strengths, indicating different degrees of conformational change of the proteins in these conditions. On the contrary, cantilevers modified by proteins, such as hemoglobin and myoglobin, that do not change conformations upon binding with analytes do not cause the cantilever deflection. These results suggest that the conformational changes of proteins may be used to develop cantilever biosensors, and the MCL system has potential for use in label-free, protein-analyte screening applications.

Animals↗
PubMed2006

Organophosphorus hydrolase multilayer modified microcantilevers for organophosphorus detection.

We report a biosensor based on organophosphorus hydrolase (OPH) multilayer modified microcantilever (MCL) for detection of organophosphorus compounds (OPs). The assay is based on substrate-dependent bending of the OPH functionalized MCLs. The cantilever bending amplitude at equilibrium was a function of the concentration of paraoxon with the dynamic range extending from 10(-7) to 10(-3)M. The lower detection limit of approximately 10(-7)M for paraoxon was an order of magnitude better than the OPH-based potentiometric and optical biosensors based on pH modulation. There was a good intra-sensor and an acceptable inter-sensor reproducibility as evidenced by the standard errors of 5% and 15%, respectively. OPs measured using this technique included parathion and diisopropyl fluorophosphate (DFP) in the order of paraoxon>DFP>parathion. The conformational change of the OPH was most likely the main origin of MCL bending.

Aryldialkylphosphatase↗
PubMed2006

Study of the near-neutral pH-sensitivity of chitosan/gelatin hydrogels by turbidimetry and microcantilever deflection.

The fundamental properties and pH-sensitivity of chitosan/gelating hydrogels were investigated using spectroscopic and microelectro mechanical (MEMS) measurement approaches. Turbidimetric titration revealed that there were electrostatic attractive interactions between tripolyphosphate (TPP), chitosan, and gelatin in the acidic pH range, depending on their degree of ionization. The pH-sensitive swelling behavior of the hydrogels was investigated by monitoring the deflection of hydrogel-coated microcantilevers, which exhibited a sensitive and repeatable response to solution pH. The deflection of the microcantilever increased as the pH decreased, and the response speed of the system exhibited a nearly linear relationship with pH. The effects of the pH and concentration of TPP solution, as well as the ratio of chitosan to gelatin in gel precursor solutions, on the pH sensitivity of the hydrogels were also investigated. It was found that the swelling of the hydrogel is mainly a result of chain relaxation of chitosan-TPP complexes caused by protonation of free amino groups in chitosan, which depends on the crosslinking density set during the formation of the network. An increase in initial crosslink density induced a decrease in swelling and pH sensitivity. It can be concluded from this study that pH-sensitive chitosan gel properties can be tuned by preparatory conditions and inclusion of gelatin. Furthermore, microcantilevers can be used as a platform for gaining increased understanding of environmentally sensitive polymers.

Biosensing Techniques↗
PubMed2006

Intramolecular triplet energy transfer in donor-acceptor molecules linked by a crown ether bridge.

Bichromophoric compounds BP-C-NP and BP-C-NBD were synthesized with benzophenone chromophore (BP) as the donor, and 2-naphthyl (NP) and norbornadiene group (NBD) as the acceptor, respectively. Their intramolecular triplet energy transfer was examined. The bridges linking the donor and acceptors in these molecules involve a crown ether moiety complexing a sodium ion. Phosphorescence quenching, flash photolysis and photosensitized isomerization experiments indicate that intramolecular triplet energy transfer occurs with rate constants of about 3.3 x 10(5) and 4.8 x 10(5) s(-1) and efficiencies of about 33 and 42 % for BP-C-NP and BP-C-NBD, respectively. Theoretical calculations indicate that these molecules adopt conformations below room temperature which allow their two-end chromophores conducive to through-space energy transfer.

Journal Article↗
PubMed2006

A calixarene based fluorescent Sr2+ and Ca2+ probe.

A fluorescent probe, PyCalix, which has two pyrene moieties at the lower rim of a calix[4]arene fixed in the cone conformation was synthesized and its complexation behavior with alkali and alkaline earth cations was studied by fluorescence spectrometry. The compound showed intramolecular excimer emission at approximately 480 nm in the fluorescence spectra. Upon complexation with alkaline earth metal cations, a decrease of excimer emission was observed. The decrease of excimer emission was accompanied by an increase of monomer emission of pyrenes at 397 nm. The order of complexation constants of PyCalix with metal ions was Sr(+ approximately Ca2+ > Ba2+ > Mg2+ > K+ > Na+ > Cs+ for all reagents. PyCalix doped polyvinyl chloride (PVC) membrane was fabricated and our results showed that this membrane can be used for selective detection of Sr2+.

Journal Article↗
PubMed2006

Microcantilevers modified by horseradish peroxidase intercalated nano-assembly for hydrogen peroxide detection.

Detection of hydrogen peroxide is of industry interest and of biological importance. Here we report a new approach to hydrogen peroxide measurement using multilayer modified microcantilevers. Through a layer-by-layer nanoassembly technique, horseradish peroxidase was intercalated into a nanoscale multilayer assembly on one surface of microcantilevers. These enzyme-functionalized microcantilevers deflected in response to hydrogen peroxide concentrations in the nanomolar level. The magnitudes of bending were proportional to the concentrations of hydrogen peroxide. Furthermore, our study also showed that microcantilever technique may be used as a novel, more sensitive tool for the study of the conformational or structural changes of enzymes or proteins on surfaces.

Adsorption↗
PubMed2005

Glucose oxidase multilayer modified microcantilevers for glucose measurement.

We report a novel enzyme-based microcantilever sensor by using layer-by-layer nanoassembly modification. A glucose oxidase (GOx) functionalized microcantilever underwent bending when it was exposed to glucose solutions. The magnitudes of bending were proportional to the concentrations of glucose. The cantilever bending was specific toward glucose, but not to other sugars such as mannose, fructose, or galactose. The flow rate effect on the cantilever bending response is also discussed. The bending mechanism was investigated, and the kinetic and thermodynamic analysis and experimental results showed that the conformational change of GOx and gluconic formation were the origin of cantilever deflection.

Enzymes, Immobilized↗
PubMed2005

Experimental and theoretical aspects of glucose measurement using a microcantilever modified by enzyme-containing polyacrylamide.

We report a glucose oxidase-containing polyacrylamide hydrogel-coated microcantilever sensor for the measurement of glucose. This enzymatic reaction of glucose results in swelling of the hydrogel due to formation of charged ions (gluconate molecules and protons). The microcantilever undergoes reversible and reproducible bending deflection upon exposure to solutions containing various glucose concentrations due to swelling or shrinking of the hydrogels. The microcantilever deflections increase when the glucose concentrations increase. A theoretical model has been built to correlate volume changes of the gel with microcantilever bending. The calculated data matched with the experimental results very well. Such hydrogel-coated microcantilevers could potentially be used to prepare microcantilever-based chemical and biological sensors when other enzymes are immobilized in the hydrogel.

Acrylic Resins↗
PubMed2004

Photon-driven nanomechanical cyclic motion.

Microcantilevers modified by a monolayer of azobenzene molecules bend up and down periodically, switched by a 365 nm UV light, as a result of the conversion of the two configurations of azobenzene molecules in the monolayer.

Journal Article↗
PubMed2004

Micromechanical measurement of membrane receptor binding for label-free drug discovery.

A potential novel binding assay based on binding-driven micromechanical motion is described. A membrane preparation containing 5-HT(3AS) receptors was used to modify a microcantilever. The modified microcantilever was found to bend on application of the naturally occurring agonist (5-hydroxytryptamine, which is also called serotonin) or the antagonist MDL-72222, but not to other similar molecules. Control experiments show that cantilevers modified by membrane preparations that do not contain 5-HT(3AS) receptors do not respond to serotonin or MDL-72222. K(d) values obtained for serotonin and MDL-72222 are identical to those obtained from radio-ligand binding assays. These results suggest that the microcantilever system has potential for use in label-free, drug screening applications.

Cell Membrane↗
PubMed2004

Detection of femtomolar concentrations of HF Using an SiO(2) microcantilever.

Femtomolar concentrations of hydrogen fluoride, a decomposition component of nerve agents, were detected using a SiO(2) microcantilever. The microcantilever underwent bending due to the reaction of HF with SiO(2). The microcantilever deflection increased as the concentration of HF increased. Other acids, such as HCl, had no effect on the deflection of the cantilever. The mechanism of reaction-induced bending and the correlation of microcantilever deflection with the HF concentration are discussed. The deflection in response to HF of a commercially available silicon cantilever was also studied, and its response was compared with that of the SiO(2) cantilever. Much less bending amplitude and sensitivity were observed for the silicon cantilever.

Biosensing Techniques↗
PubMed2004

An anti E. coli O157:H7 antibody-immobilized microcantilever for the detection of Escherichia coli (E. coli).

A silicon microcantilever sensor was developed for the detection of Escherichia coli O157:H7. The microcantilever was modified by anti-E. coli O157:H7 antibodies on the silicon surface of the cantilever. When the aquaria E. coli O157:H7 positive sample is injected into the fluid cell where the microcantilever is held, the microcantilever bends upon the recognition of the E. coli O157:H7 antigen by the antibodies on the surface of the microcantilever. A negative control sample that does not contain E. coli O157:H7 antigen did not cause any bending of the microcantilever. The detection limit of the sensor was 1 x 10(6) cfu/mL when the assay time was < 2 h.

Adsorption↗
PubMed2004

Detection of Pb2+ using a hydrogel swelling microcantilever sensor.

Hydrogels containing benzo-18-crown-6 were used to modify microcantilevers for measurements of the concentration of Pb2+ in aqueous solutions. These microcantilevers undergo bending deflection upon exposure to solutions containing various Pb2+ concentrations as the result of a swelling of the hydrogels. It was found that a concentration of 10(-6) M Pb2+ can be detected using this technology. Other cations, such as Na+, have no effect on the deflection of this cantilever. The cation K+, which also complexes with benzo-18-crown-6, could interfere with Pb2+ detection, but only at high concentrations (> 10(-4) M).

Journal Article↗
PubMed2003

Detection of CrO4(2-) using a hydrogel swelling microcantilever sensor.

Hydrogels containing various mounts of tetraalkylammonium salts were used to modify microcantilevers for measurements of the concentration of CrO4(2-) in aqueous solutions. These microcantilevers undergo bending deflection upon exposure to solutions containing various CrO4(2-) concentrations as a result of swelling or shrinking of the hydrogels. The microcantilever deflection as a function of the concentration of CrO4(2-) ions is nearly linear in most concentration ranges. It was found that a concentration of 10(-11) M CrO4(2-) can be detected using this technology in a fluid cell. Other ions, such as Br-, HPO4(2-), and NO3-, have minimal effect on the deflection of this cantilever. The anions SO4(2-) and CO3(2-) could interfere with the CrO4(2-) detection, but only at high concentrations (> 10(-5) M). Such hydrogel-coated microcantilevers could potentially be used to prepare microcantilever-based chemical and biological sensors when molecular recognition agents are immobilized in the hydrogel.

Journal Article↗
PubMed2002

Detection of Hg2+ using microcantilever sensors.

Trace amounts of Hg2+ are detected by using a microcantilever coated with gold. The microcantilever undergoes bending due to accumulation of Hg2+ on the gold surface. It is found that a concentration of 10(-11) M Hg2+ can be detected using this technology. Other cations, such as K+, Na+, Pb2+, Zn2+, Ni2, Cd2+, Cu2+, and Ca2+ have little or no effect on the deflection of the cantilever. The selectivity of the Hg2+ sensor could be improved by coating the gold surface of microcantilever with a self-assembled monolayer of a long-chain thiol compound.

Adsorption↗