Siu-Tung Yau - Academia.edu (original) (raw)

Papers by Siu-Tung Yau

Research paper thumbnail of Fundamentals and Control Strategies for Nucleation of Protein Crystals in Solution

Research paper thumbnail of Rapid diagnosis of bloodstream infections using a culture-free phenotypic platform

Communications medicine, Apr 23, 2024

Background Bloodstream infections (BSIs) are a life-threatening acute medical condition and curre... more Background Bloodstream infections (BSIs) are a life-threatening acute medical condition and current diagnostics for BSIs suffer from long turnaround time (TAT). Here we show the validation of a rapid detection-analysis platform (RDAP) for the diagnosis of BSIs performed on clinical blood samples Methods The validation was performed on a cohort of 59 clinical blood samples, including positive culture samples, which indicated confirmed bloodstream infections, and negative culture samples. The bacteria in the positive culture samples included Gram-positive and Gram-negative pathogenic species. RDAP is based on an electrochemical sandwich immunoassay with voltage-controlled signal amplification, which provides an ultra-low limit of detection (4 CFU/mL), allowing the platform to detect and identify bacteria without requiring culture and perform phenotypic antibiotic susceptibility testing (AST) with only 1-2 h of antibiotic exposure. The preliminary diagnostic performance of RDAP was compared with that of standard commercial diagnostic technologies. Results Using a typical clinical microbiology laboratory diagnostic workflow that involved sample culture, agar plating, bacteria identification using matrix-assisted laser desorption ionization time-of-flight (MALDI TOF) mass spectrometry, and AST using MicroScan as a clinical diagnostic reference, RDAP showed diagnostic accuracy of 93.3% and 95.4% for detection-identification and AST, respectively. However, RDAP provided results at least 15 h faster. Conclusions This study shows the preliminary feasibility of using RDAP to rapidly diagnose BSIs, including AST. Limitations and potential mitigation strategies for clinical translation of the present RDAP prototype are discussed. The results of this clinical feasibility study indicate an approach to provide near real-time diagnostic information for clinicians to significantly enhance the treatment outcome of BSIs.

Research paper thumbnail of Enhanced Growth of Microalgae and Production of Lipids via Electrostatically Controlled Photosynthesis

ACS Sustainable Chemistry & Engineering

Research paper thumbnail of Mediator-less immunodetection with voltage-controlled intrinsic amplification for ultrasensitive and rapid detection of microorganism pathogens

A mediator-less immunodetection method for microorganisms is realized by incorporating the newly ... more A mediator-less immunodetection method for microorganisms is realized by incorporating the newly developed field-effect enzymatic detection (FEED) technique with the conventional electrochemical immunosensing approach. The gating voltage of FEED facilitates the transduction of electrical signal through the bulky immune complex so that the detection does not rely on the use of mediators or other diffusional substances. The voltage-controlled intrinsic amplification provided by the detection system allows detection in low-concentration samples without target pre-enrichment, leading to ultrasensitive and rapid detection. The detection approach is demonstrated with E. coliO157:H7, a model microorganism, in milk with an estimated detection limit of 20 CFU mL−1 (where CFU is a colony-forming unit) without performing sample pre-enrichment and centrifugation of sample followed by the resuspension of the pellet in a buffer solution, resulting in a significantly shortened assay time of 67 min...

Research paper thumbnail of Repository Citation

Detection of prostate specific antigen in serum at the femto-gram per milliliter level using the ... more Detection of prostate specific antigen in serum at the femto-gram per milliliter level using the intrinsic amplification of a field-effect enzymatic immuno-sensing system

Research paper thumbnail of Real Time In-situ Monitoring of Ferritin Crystallization with Molecular Resolution

Research paper thumbnail of What Would Gibbs Do If he Were Thinking of Nucleation of Protein Solid Phases

Research paper thumbnail of Fabrication of nanostructures with the scanning tunneling microscope and the laser

A technique of making nanometer-scale structures on surfaces is developed. The technique combines... more A technique of making nanometer-scale structures on surfaces is developed. The technique combines two of the most advanced technologies: the laser and the scanning tunneling microscope (STM). Laser radiation is used to break the chemical bonds of gas-phase trimethylaluminum molecules to free aluminum atoms in the region of the tunneling gap of the STM. The atoms are subsequently selectively excited and ionized. The ions are then driven softly toward the surface where they are deposited by the field in the tunneling gap of the microscope. Deposits as small as 1nmx1nm were made on graphite substrates. The technique is also capable of addressable erasing.The more familiar technique of using voltage pulses applied to the STM tunneling tip to fabricate nanostructures was also studied. Both deposits and holes were made. The voltage threshold and other features of the fabrication process were studied as a function of the tip-surface biasing voltage and the tunneling current. The studies show that the structures were formed by bombardment of the graphite surface by ions produced by electron-assisted field ionization localized in the region of the tunneling gap. This technique was combined with the STM-Laser technique to modify surfaces.U of I OnlyETDs are only available to UIUC Users without author permissio

Research paper thumbnail of Spatially selective immobilization of ferritin using solid–solution interfacial interactions

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2005

Spatially selective immobilization of ferritin, an iron-storage protein, on a silicon surface usi... more Spatially selective immobilization of ferritin, an iron-storage protein, on a silicon surface using a Si-SiO 2 template is demonstrated. The material-specific immobilization of the protein is achieved by controlling physical forces at the solution-solid interface between a ferritin solution and the template. The electrostatic interaction and hydrophobic interaction between ferritin molecules and the two kinds of materials of the template can be tuned to achieve adsorption of ferritin only on Si. This method was used to generate spatially confined assemblies of ferritin on the nanoscale and on the micron scale.

Research paper thumbnail of Detection of α-Methylacyl-CoA Racemase in Serum and Urine Using a Highly Sensitive Electrochemical Immunodetector

Electroanalysis, 2014

ABSTRACT The detection of α-methylacyl-CoA racemase (AMACR), a novel biomarker for prostate cance... more ABSTRACT The detection of α-methylacyl-CoA racemase (AMACR), a novel biomarker for prostate cancer, is demonstrated in serum and urine using a novel immuno-detection method. The detection system consists of a three-electrode conventional electrochemical cell modified with a gating electrode for applying a gating voltage VG to the immune complex immobilized on the working electrode to provide signal amplification. The detection system is realized by integrating gating electrodes with screen-printed electrodes. This detection method does not require involved sample preparation procedures. The detection was demonstrated in serum and urine samples on the nanogram/mL level with VG equal to 0.6 V. Detection in serum was also performed on the picogram/mL level with a limit of 100 picogram/mL with VG=0.6 V being a necessary condition.

Research paper thumbnail of Parallel fabrication on chemically etched silicon using scanning tunneling microscopy

Ultramicroscopy, 1992

We use a scanning tunneling microscope to fabricate nanometer-scale lithographic structures on ch... more We use a scanning tunneling microscope to fabricate nanometer-scale lithographic structures on chemically etched silicon sample. The process is believed to proceed by electron polymerization and activation of the reaction of the absorbed layer with the silicon surface. We study various aspects of the process, including resolution, density of adsorbates, and tip shape. We present results on the use of this method for fabrication of lines, and results which show parallel fabrication using tips that have multiple sharp peaks.

Research paper thumbnail of Construction of low-dimensional assemblies of nanoparticles

Nanotechnology, 2003

ABSTRACT A two-step method for constructing nanometre-scale architectural structures of nanoparti... more ABSTRACT A two-step method for constructing nanometre-scale architectural structures of nanoparticles on a solid surface is demonstrated. The method depends on physical processes between a colloid of nanoparticles and a hydrophobic surface that contains recess patterns. The effects of sedimentation of particles and of dewetting of the surface result in deposition of nanoparticles only within the patterns. This method has been used to generate spatially confined monolayers of nanoparticles, to assemble a small number of particles to each point of a 2D array and to construct 1D chains of interconnected particles on a surface. This versatile method can be used to generate architectural structures on a solid surface on various length scales.

Research paper thumbnail of Scanning Tunneling Microscopy of Ferritin Nanostructures

Modern Physics Letters B, 1995

In molecular electronics, components and circuits are made of biological molecules.1 It is import... more In molecular electronics, components and circuits are made of biological molecules.1 It is important to study how the molecules arrange themselves on a substrate and to arrange them artificially. The ferritin molecule is a good candidate for making molecular devices. Previously, transmission electron microscopy was used to image only the metallic core of the ferritin molecule. We use scanning tunneling microscopy to study the behavior of ferritin deposited on a surface by imaging its protein shell. We have observed different kinds of ferritin aggregates as well as single molecules under different deposition conditions. For the first time ordered self-assemble of ferritin aggregates was observed. The aggregates were also found to be arranged in artificially made patterns. We suggest a possible mechanism of the formation of the observed structures.

Research paper thumbnail of Supercapacitor electrodes based on polyaniline–silicon nanoparticle composite

Journal of Power Sources, 2010

... [4] E. Frackowiak, V. Khomenko, K. Jurewicz, K. Lota and F. Beguin, J. Power Sources 153 (200... more ... [4] E. Frackowiak, V. Khomenko, K. Jurewicz, K. Lota and F. Beguin, J. Power Sources 153 (2006), p. 413. ... [6] B. Rajesh, KR Thampi, JM Bonard, cHJ Mathieu, N. Xanthopoulos and B. Viswanathand, Electrochem. Solid-State Lett. 7 (2004), p. A404. ...

Research paper thumbnail of Inlaying Nanoscale Surface Recess Patterns with Nanoscale Objects

Journal of Nanoscience and Nanotechnology, 2006

A simple and versatile approach to constructing patterns on a solid surface using nanoscale objec... more A simple and versatile approach to constructing patterns on a solid surface using nanoscale objects is demonstrated. The approach is essentially an inlaying process, in which recess patterns fabricated on a surface are selectively filled with nanoscale objects. The objects are anchored firmly on the surface due to the spatial confinement provided by the recess structures. Protein molecules and inorganic nanoparticles are used in this demonstration. Cyclic voltammetry is used to detect electron transfer signals from patterns of protein molecules. The approach suggests a potentially fast, high-throughput and versatile technique for constructing architectural structures on a solid surface using nanoscale objects.

Research paper thumbnail of Soluble silicon nanoparticles–polyaniline capsules for biosensing and imaging

Journal of Materials Research, 2012

ABSTRACT We used miniemulsion to synthesize novel water-soluble dispersion of nanocapsules with a... more ABSTRACT We used miniemulsion to synthesize novel water-soluble dispersion of nanocapsules with a polyaniline (PANI) shell and luminescent ultrasmall Si nanoparticle core with diameters of 50–300 nm. The capsules are functionalized with aromatic sulfonic acid. The capsules may be reconstituted in thin films or structured surfaces. The stability of the luminescence and dispersion of the capsules is studied under a wide range of pH conditions. The multiplicity of nanoparticles in the core provides highly amplified and reproducible signal for luminescence-based imaging using standard fluorescence microscopy, while the PANI shell allows a variety of routes for functionalization as well as electrical interrogation, which enables a wide range of biosensing/imaging applications.

Research paper thumbnail of Are protein crystallization mechanisms relevant to understanding and control of polymerization of deoxyhemoglobin S?

Journal of Crystal Growth, 2001

ABSTRACT We investigated the homogeneous nucleation and subsequent evolution of polymers of sickl... more ABSTRACT We investigated the homogeneous nucleation and subsequent evolution of polymers of sickle cell hemoglobin (HbS) using differential interference contrast (DIC) microscopy. The same technique was employed to determine the liquid–liquid separation boundaries for a variety of conditions in solution of sickle cell and normal human hemoglobin. The HbS polymers were also imaged using atomic force microscopy. We found that the location of Liquid–Liquid phase boundary under conditions that mimic those in the erythrocytes is consistent with previous determinations of the spinodal for this phase transition. Increasing the ionic strength shifts this phase boundary to significantly lower temperatures and Hb concentrations. We also found that the nucleation of individual HbS fibers indicates that the process is random and follows statistics similar to those established for nucleation of crystals or liquid droplets from vapors.

Research paper thumbnail of Enzyme-immobilized SiO2–Si electrode: Fast interfacial electron transfer with preserved enzymatic activity

Applied Physics Letters, 2005

ABSTRACT The enzyme, glucose oxidase (GOx), is immobilized using electrostatic interaction on the... more ABSTRACT The enzyme, glucose oxidase (GOx), is immobilized using electrostatic interaction on the native oxide of heavily doped n-type silicon. Voltammetric measurement shows that the immobilized GOx gives rise to a very fast enzyme-silicon interfacial electron transfer rate constant of 7.9 s−1. The measurement also suggests that the enzyme retains its native conformation when immobilized on the silicon surface. The preserved native conformation of GOx is further confirmed by testing the enzymatic activity of the immobilized GOx using glucose. The GOx-immobilized silicon is shown to behave as a glucose sensor that detects glucose with concentrations as low as 50 μM.

Research paper thumbnail of A prototype protein field-effect transistor

Applied Physics Letters, 2005

ABSTRACT Electrical conduction in a macroscopic assembly of apoferritin, a non-redox protein, has... more ABSTRACT Electrical conduction in a macroscopic assembly of apoferritin, a non-redox protein, has been characterized using a three-terminal prototype device. Our result shows an ohmic conduction near zero bias. The ohmic conduction can be controlled using an electric field applied to the protein assembly via the gate terminal of the device. The transconductance of the protein device shows a highly nonlinear dependence on the gate voltage. The transconductance curve indicates that the device has the attributes of an n-channel metal-oxide-semiconductor field-effect transistor with electrons as charge carriers. The input/output dynamic response of the device has been demonstrated.

Research paper thumbnail of Laser-assisted deposition of nanometer structures using a scanning tunneling microscope

Applied Physics Letters, 1990

Nanometer-scale deposits as small as 1 nm have been made on graphite surfaces using laser-induced... more Nanometer-scale deposits as small as 1 nm have been made on graphite surfaces using laser-induced multiphoton fragmentation and ionization of trimethylaluminum (TMA) molecules in the tunneling junction of a scanning tunneling microscope. Laser radiation generates ions, which are guided to the surface by the electric field between the tip and the surface. The resolution of this technique is limited by the extent of the field in the tunneling junction.

Research paper thumbnail of Fundamentals and Control Strategies for Nucleation of Protein Crystals in Solution

Research paper thumbnail of Rapid diagnosis of bloodstream infections using a culture-free phenotypic platform

Communications medicine, Apr 23, 2024

Background Bloodstream infections (BSIs) are a life-threatening acute medical condition and curre... more Background Bloodstream infections (BSIs) are a life-threatening acute medical condition and current diagnostics for BSIs suffer from long turnaround time (TAT). Here we show the validation of a rapid detection-analysis platform (RDAP) for the diagnosis of BSIs performed on clinical blood samples Methods The validation was performed on a cohort of 59 clinical blood samples, including positive culture samples, which indicated confirmed bloodstream infections, and negative culture samples. The bacteria in the positive culture samples included Gram-positive and Gram-negative pathogenic species. RDAP is based on an electrochemical sandwich immunoassay with voltage-controlled signal amplification, which provides an ultra-low limit of detection (4 CFU/mL), allowing the platform to detect and identify bacteria without requiring culture and perform phenotypic antibiotic susceptibility testing (AST) with only 1-2 h of antibiotic exposure. The preliminary diagnostic performance of RDAP was compared with that of standard commercial diagnostic technologies. Results Using a typical clinical microbiology laboratory diagnostic workflow that involved sample culture, agar plating, bacteria identification using matrix-assisted laser desorption ionization time-of-flight (MALDI TOF) mass spectrometry, and AST using MicroScan as a clinical diagnostic reference, RDAP showed diagnostic accuracy of 93.3% and 95.4% for detection-identification and AST, respectively. However, RDAP provided results at least 15 h faster. Conclusions This study shows the preliminary feasibility of using RDAP to rapidly diagnose BSIs, including AST. Limitations and potential mitigation strategies for clinical translation of the present RDAP prototype are discussed. The results of this clinical feasibility study indicate an approach to provide near real-time diagnostic information for clinicians to significantly enhance the treatment outcome of BSIs.

Research paper thumbnail of Enhanced Growth of Microalgae and Production of Lipids via Electrostatically Controlled Photosynthesis

ACS Sustainable Chemistry & Engineering

Research paper thumbnail of Mediator-less immunodetection with voltage-controlled intrinsic amplification for ultrasensitive and rapid detection of microorganism pathogens

A mediator-less immunodetection method for microorganisms is realized by incorporating the newly ... more A mediator-less immunodetection method for microorganisms is realized by incorporating the newly developed field-effect enzymatic detection (FEED) technique with the conventional electrochemical immunosensing approach. The gating voltage of FEED facilitates the transduction of electrical signal through the bulky immune complex so that the detection does not rely on the use of mediators or other diffusional substances. The voltage-controlled intrinsic amplification provided by the detection system allows detection in low-concentration samples without target pre-enrichment, leading to ultrasensitive and rapid detection. The detection approach is demonstrated with E. coliO157:H7, a model microorganism, in milk with an estimated detection limit of 20 CFU mL−1 (where CFU is a colony-forming unit) without performing sample pre-enrichment and centrifugation of sample followed by the resuspension of the pellet in a buffer solution, resulting in a significantly shortened assay time of 67 min...

Research paper thumbnail of Repository Citation

Detection of prostate specific antigen in serum at the femto-gram per milliliter level using the ... more Detection of prostate specific antigen in serum at the femto-gram per milliliter level using the intrinsic amplification of a field-effect enzymatic immuno-sensing system

Research paper thumbnail of Real Time In-situ Monitoring of Ferritin Crystallization with Molecular Resolution

Research paper thumbnail of What Would Gibbs Do If he Were Thinking of Nucleation of Protein Solid Phases

Research paper thumbnail of Fabrication of nanostructures with the scanning tunneling microscope and the laser

A technique of making nanometer-scale structures on surfaces is developed. The technique combines... more A technique of making nanometer-scale structures on surfaces is developed. The technique combines two of the most advanced technologies: the laser and the scanning tunneling microscope (STM). Laser radiation is used to break the chemical bonds of gas-phase trimethylaluminum molecules to free aluminum atoms in the region of the tunneling gap of the STM. The atoms are subsequently selectively excited and ionized. The ions are then driven softly toward the surface where they are deposited by the field in the tunneling gap of the microscope. Deposits as small as 1nmx1nm were made on graphite substrates. The technique is also capable of addressable erasing.The more familiar technique of using voltage pulses applied to the STM tunneling tip to fabricate nanostructures was also studied. Both deposits and holes were made. The voltage threshold and other features of the fabrication process were studied as a function of the tip-surface biasing voltage and the tunneling current. The studies show that the structures were formed by bombardment of the graphite surface by ions produced by electron-assisted field ionization localized in the region of the tunneling gap. This technique was combined with the STM-Laser technique to modify surfaces.U of I OnlyETDs are only available to UIUC Users without author permissio

Research paper thumbnail of Spatially selective immobilization of ferritin using solid–solution interfacial interactions

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2005

Spatially selective immobilization of ferritin, an iron-storage protein, on a silicon surface usi... more Spatially selective immobilization of ferritin, an iron-storage protein, on a silicon surface using a Si-SiO 2 template is demonstrated. The material-specific immobilization of the protein is achieved by controlling physical forces at the solution-solid interface between a ferritin solution and the template. The electrostatic interaction and hydrophobic interaction between ferritin molecules and the two kinds of materials of the template can be tuned to achieve adsorption of ferritin only on Si. This method was used to generate spatially confined assemblies of ferritin on the nanoscale and on the micron scale.

Research paper thumbnail of Detection of α-Methylacyl-CoA Racemase in Serum and Urine Using a Highly Sensitive Electrochemical Immunodetector

Electroanalysis, 2014

ABSTRACT The detection of α-methylacyl-CoA racemase (AMACR), a novel biomarker for prostate cance... more ABSTRACT The detection of α-methylacyl-CoA racemase (AMACR), a novel biomarker for prostate cancer, is demonstrated in serum and urine using a novel immuno-detection method. The detection system consists of a three-electrode conventional electrochemical cell modified with a gating electrode for applying a gating voltage VG to the immune complex immobilized on the working electrode to provide signal amplification. The detection system is realized by integrating gating electrodes with screen-printed electrodes. This detection method does not require involved sample preparation procedures. The detection was demonstrated in serum and urine samples on the nanogram/mL level with VG equal to 0.6 V. Detection in serum was also performed on the picogram/mL level with a limit of 100 picogram/mL with VG=0.6 V being a necessary condition.

Research paper thumbnail of Parallel fabrication on chemically etched silicon using scanning tunneling microscopy

Ultramicroscopy, 1992

We use a scanning tunneling microscope to fabricate nanometer-scale lithographic structures on ch... more We use a scanning tunneling microscope to fabricate nanometer-scale lithographic structures on chemically etched silicon sample. The process is believed to proceed by electron polymerization and activation of the reaction of the absorbed layer with the silicon surface. We study various aspects of the process, including resolution, density of adsorbates, and tip shape. We present results on the use of this method for fabrication of lines, and results which show parallel fabrication using tips that have multiple sharp peaks.

Research paper thumbnail of Construction of low-dimensional assemblies of nanoparticles

Nanotechnology, 2003

ABSTRACT A two-step method for constructing nanometre-scale architectural structures of nanoparti... more ABSTRACT A two-step method for constructing nanometre-scale architectural structures of nanoparticles on a solid surface is demonstrated. The method depends on physical processes between a colloid of nanoparticles and a hydrophobic surface that contains recess patterns. The effects of sedimentation of particles and of dewetting of the surface result in deposition of nanoparticles only within the patterns. This method has been used to generate spatially confined monolayers of nanoparticles, to assemble a small number of particles to each point of a 2D array and to construct 1D chains of interconnected particles on a surface. This versatile method can be used to generate architectural structures on a solid surface on various length scales.

Research paper thumbnail of Scanning Tunneling Microscopy of Ferritin Nanostructures

Modern Physics Letters B, 1995

In molecular electronics, components and circuits are made of biological molecules.1 It is import... more In molecular electronics, components and circuits are made of biological molecules.1 It is important to study how the molecules arrange themselves on a substrate and to arrange them artificially. The ferritin molecule is a good candidate for making molecular devices. Previously, transmission electron microscopy was used to image only the metallic core of the ferritin molecule. We use scanning tunneling microscopy to study the behavior of ferritin deposited on a surface by imaging its protein shell. We have observed different kinds of ferritin aggregates as well as single molecules under different deposition conditions. For the first time ordered self-assemble of ferritin aggregates was observed. The aggregates were also found to be arranged in artificially made patterns. We suggest a possible mechanism of the formation of the observed structures.

Research paper thumbnail of Supercapacitor electrodes based on polyaniline–silicon nanoparticle composite

Journal of Power Sources, 2010

... [4] E. Frackowiak, V. Khomenko, K. Jurewicz, K. Lota and F. Beguin, J. Power Sources 153 (200... more ... [4] E. Frackowiak, V. Khomenko, K. Jurewicz, K. Lota and F. Beguin, J. Power Sources 153 (2006), p. 413. ... [6] B. Rajesh, KR Thampi, JM Bonard, cHJ Mathieu, N. Xanthopoulos and B. Viswanathand, Electrochem. Solid-State Lett. 7 (2004), p. A404. ...

Research paper thumbnail of Inlaying Nanoscale Surface Recess Patterns with Nanoscale Objects

Journal of Nanoscience and Nanotechnology, 2006

A simple and versatile approach to constructing patterns on a solid surface using nanoscale objec... more A simple and versatile approach to constructing patterns on a solid surface using nanoscale objects is demonstrated. The approach is essentially an inlaying process, in which recess patterns fabricated on a surface are selectively filled with nanoscale objects. The objects are anchored firmly on the surface due to the spatial confinement provided by the recess structures. Protein molecules and inorganic nanoparticles are used in this demonstration. Cyclic voltammetry is used to detect electron transfer signals from patterns of protein molecules. The approach suggests a potentially fast, high-throughput and versatile technique for constructing architectural structures on a solid surface using nanoscale objects.

Research paper thumbnail of Soluble silicon nanoparticles–polyaniline capsules for biosensing and imaging

Journal of Materials Research, 2012

ABSTRACT We used miniemulsion to synthesize novel water-soluble dispersion of nanocapsules with a... more ABSTRACT We used miniemulsion to synthesize novel water-soluble dispersion of nanocapsules with a polyaniline (PANI) shell and luminescent ultrasmall Si nanoparticle core with diameters of 50–300 nm. The capsules are functionalized with aromatic sulfonic acid. The capsules may be reconstituted in thin films or structured surfaces. The stability of the luminescence and dispersion of the capsules is studied under a wide range of pH conditions. The multiplicity of nanoparticles in the core provides highly amplified and reproducible signal for luminescence-based imaging using standard fluorescence microscopy, while the PANI shell allows a variety of routes for functionalization as well as electrical interrogation, which enables a wide range of biosensing/imaging applications.

Research paper thumbnail of Are protein crystallization mechanisms relevant to understanding and control of polymerization of deoxyhemoglobin S?

Journal of Crystal Growth, 2001

ABSTRACT We investigated the homogeneous nucleation and subsequent evolution of polymers of sickl... more ABSTRACT We investigated the homogeneous nucleation and subsequent evolution of polymers of sickle cell hemoglobin (HbS) using differential interference contrast (DIC) microscopy. The same technique was employed to determine the liquid–liquid separation boundaries for a variety of conditions in solution of sickle cell and normal human hemoglobin. The HbS polymers were also imaged using atomic force microscopy. We found that the location of Liquid–Liquid phase boundary under conditions that mimic those in the erythrocytes is consistent with previous determinations of the spinodal for this phase transition. Increasing the ionic strength shifts this phase boundary to significantly lower temperatures and Hb concentrations. We also found that the nucleation of individual HbS fibers indicates that the process is random and follows statistics similar to those established for nucleation of crystals or liquid droplets from vapors.

Research paper thumbnail of Enzyme-immobilized SiO2–Si electrode: Fast interfacial electron transfer with preserved enzymatic activity

Applied Physics Letters, 2005

ABSTRACT The enzyme, glucose oxidase (GOx), is immobilized using electrostatic interaction on the... more ABSTRACT The enzyme, glucose oxidase (GOx), is immobilized using electrostatic interaction on the native oxide of heavily doped n-type silicon. Voltammetric measurement shows that the immobilized GOx gives rise to a very fast enzyme-silicon interfacial electron transfer rate constant of 7.9 s−1. The measurement also suggests that the enzyme retains its native conformation when immobilized on the silicon surface. The preserved native conformation of GOx is further confirmed by testing the enzymatic activity of the immobilized GOx using glucose. The GOx-immobilized silicon is shown to behave as a glucose sensor that detects glucose with concentrations as low as 50 μM.

Research paper thumbnail of A prototype protein field-effect transistor

Applied Physics Letters, 2005

ABSTRACT Electrical conduction in a macroscopic assembly of apoferritin, a non-redox protein, has... more ABSTRACT Electrical conduction in a macroscopic assembly of apoferritin, a non-redox protein, has been characterized using a three-terminal prototype device. Our result shows an ohmic conduction near zero bias. The ohmic conduction can be controlled using an electric field applied to the protein assembly via the gate terminal of the device. The transconductance of the protein device shows a highly nonlinear dependence on the gate voltage. The transconductance curve indicates that the device has the attributes of an n-channel metal-oxide-semiconductor field-effect transistor with electrons as charge carriers. The input/output dynamic response of the device has been demonstrated.

Research paper thumbnail of Laser-assisted deposition of nanometer structures using a scanning tunneling microscope

Applied Physics Letters, 1990

Nanometer-scale deposits as small as 1 nm have been made on graphite surfaces using laser-induced... more Nanometer-scale deposits as small as 1 nm have been made on graphite surfaces using laser-induced multiphoton fragmentation and ionization of trimethylaluminum (TMA) molecules in the tunneling junction of a scanning tunneling microscope. Laser radiation generates ions, which are guided to the surface by the electric field between the tip and the surface. The resolution of this technique is limited by the extent of the field in the tunneling junction.