The University of Washington, Seattle, WA, B.Sc. (Chemistry & Biochemistry), 1989-1992
The University of Chicago, Chicago, IL, Ph.D. (Bioorganic Chemistry), 1992-1996
Harvard University, Boston, MA, Postdoctoral Research Fellow (Biochemistry and Bioorganic Chemistry), 1997-1999
Assistant Professor, City University of New York, York College and Graduate Center, 1999-2003
Associate Professor, City University of New York, York College and Graduate Center, 2003-2004
Principal Scientist, Lawrence Livermore National Laboratory, 2004-2008
Chief BioScientist, Micropoint Bioscience Inc, 2008-2010
Senior Research Engineer/Scientist, Stanford University, 2010-present
Director, Uytengsu Teaching Center, Shriram Center, 2015-present
Manager, Soft & Hybrid Materials Shared Facility, Stanford Nano Shared Facility, 2010-present
Manager & Instructor, Dept of Chemical Engineering Teaching Lab, 2010-present
Highly stretchable polymer semiconductor films through the nanoconfinement effect
2017; 355 (6320): 59-?
Soft and conformable wearable electronics require stretchable semiconductors, but existing ones typically sacrifice charge transport mobility to achieve stretchability. We explore a concept based on the nanoconfinement of polymers to substantially improve the stretchability of polymer semiconductors, without affecting charge transport mobility. The increased polymer chain dynamics under nanoconfinement significantly reduces the modulus of the conjugated polymer and largely delays the onset of crack formation under strain. As a result, our fabricated semiconducting film can be stretched up to 100% strain without affecting mobility, retaining values comparable to that of amorphous silicon. The fully stretchable transistors exhibit high biaxial stretchability with minimal change in on current even when poked with a sharp object. We demonstrate a skinlike finger-wearable driver for a light-emitting diode.
View details for DOI 10.1126/science.aah4496
View details for Web of Science ID 000391739900042
View details for PubMedID 28059762
Intrinsically stretchable and healable semiconducting polymer for organic transistors
2016; 539 (7629): 411-415
Thin-film field-effect transistors are essential elements of stretchable electronic devices for wearable electronics. All of the materials and components of such transistors need to be stretchable and mechanically robust. Although there has been recent progress towards stretchable conductors, the realization of stretchable semiconductors has focused mainly on strain-accommodating engineering of materials, or blending of nanofibres or nanowires into elastomers. An alternative approach relies on using semiconductors that are intrinsically stretchable, so that they can be fabricated using standard processing methods. Molecular stretchability can be enhanced when conjugated polymers, containing modified side-chains and segmented backbones, are infused with more flexible molecular building blocks. Here we present a design concept for stretchable semiconducting polymers, which involves introducing chemical moieties to promote dynamic non-covalent crosslinking of the conjugated polymers. These non-covalent crosslinking moieties are able to undergo an energy dissipation mechanism through breakage of bonds when strain is applied, while retaining high charge transport abilities. As a result, our polymer is able to recover its high field-effect mobility performance (more than 1 square centimetre per volt per second) even after a hundred cycles at 100 per cent applied strain. Organic thin-film field-effect transistors fabricated from these materials exhibited mobility as high as 1.3 square centimetres per volt per second and a high on/off current ratio exceeding a million. The field-effect mobility remained as high as 1.12 square centimetres per volt per second at 100 per cent strain along the direction perpendicular to the strain. The field-effect mobility of damaged devices can be almost fully recovered after a solvent and thermal healing treatment. Finally, we successfully fabricated a skin-inspired stretchable organic transistor operating under deformations that might be expected in a wearable device.
View details for DOI 10.1038/nature20102
View details for Web of Science ID 000388161700050
View details for PubMedID 27853213
Hierarchical N-Doped Carbon as CO2 Adsorbent with High CO2 Selectivity from Rationally Designed Polypyrrole Precursor
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2016; 138 (3): 1001-1009
Carbon capture and sequestration from point sources is an important component in the CO2 emission mitigation portfolio. In particular, sorbents with both high capacity and selectivity are required for reducing the cost of carbon capture. Although physisorbents have the advantage of low energy consumption for regeneration, it remains a challenge to obtain both high capacity and sufficient CO2/N2 selectivity at the same time. Here, we report the controlled synthesis of a novel N-doped hierarchical carbon that exhibits record-high Henry's law CO2/N2 selectivity among physisorptive carbons while having a high CO2 adsorption capacity. Specifically, our synthesis involves the rational design of a modified pyrrole molecule that can co-assemble with the soft Pluronic template via hydrogen bonding and electrostatic interactions to give rise to mesopores followed by carbonization. The low-temperature carbonization and activation processes allow for the development of ultrasmall pores (d < 0.5 nm) and preservation of nitrogen moieties, essential for enhanced CO2 affinity. Furthermore, our described work provides a strategy to initiate developments of rationally designed porous conjugated polymer structures and carbon-based materials for various potential applications.
View details for DOI 10.1021/jacs.5b11955
View details for Web of Science ID 000369044400047
View details for PubMedID 26717034
- A chameleon-inspired stretchable electronic skin with interactive colour changing controlled by tactile sensing NATURE COMMUNICATIONS 2015; 6
Highly skin-conformal microhairy sensor for pulse signal amplification.
2015; 27 (4): 634-640
A bioinspired microhairy sensor is developed to enable ultraconformability on nonflat surfaces and significant enhancement in the signal-to-noise ratio of the retrieved signals. The device shows ≈12 times increase in the signal-to-noise ratio in the generated capacitive signals, allowing the ultraconformal microhair pressure sensors to be capable of measuring weak pulsations of internal jugular venous pulses stemming from a human neck.
View details for DOI 10.1002/adma.201403807
View details for PubMedID 25358966
Electronic Readout Enzyme-Linked Immunosorbent Assay with Organic Field-Effect Transistors as a Preeclampsia Prognostic
2014; 26 (35): 6138-?
Organic field-effect transistor (OFET) sensors can meet the need for portable and real-time diagnostics. An electronicreadout enzyme-linked immunosorbent assay using OFETs for the detection of a panel of three biomarkers in complex media to create a pre-eclampsia prognostic is demonstrated, along with biodetection utilizing a fully inkjet-printed and flexible OFET to underscore our ability to produce disposable devices.
View details for DOI 10.1002/adma.201401829
View details for Web of Science ID 000342148600013
View details for PubMedID 25047764
Large-area, transparent, and flexible infrared photodetector fabricated using p-N junctions formed by N-doping chemical vapor deposition grown graphene.
2014; 14 (7): 3702-3708
Graphene is a highly promising material for high speed, broadband, and multicolor photodetection. Because of its lack of bandgap, individually gated P- and N-regions are needed to fabricate photodetectors. Here we report a technique for making a large-area photodetector on the basis of controllable fabrication of graphene P-N junctions. Our selectively doped chemical vapor deposition (CVD) graphene photodetector showed a ∼5% modulation of conductance under global IR irradiation. By comparing devices of various geometries, we identify that both the homogeneous and the P-N junction regions contribute competitively to the photoresponse. Furthermore, we demonstrate that our two-terminal graphene photodetector can be fabricated on both transparent and flexible substrates without the need for complex fabrication processes used in electrically gated three-terminal devices. This represents the first demonstration of a fully transparent and flexible graphene-based IR photodetector that exhibits both good photoresponsivity and high bending capability. This simple approach should facilitate the development of next generation high-performance IR photodetectors.
View details for DOI 10.1021/nl500443j
View details for PubMedID 24927382
A flexible bimodal sensor array for simultaneous sensing of pressure and temperature.
2014; 26 (5): 796-804
Diverse signals generated from the sensing elements embedded in flexible electronic skins (e-skins) are typically interfered by strain energy generated through processes such as touching, bending, stretching or twisting. Herein, we demonstrate a flexible bimodal sensor that can separate a target signal from the signal by mechanical strain through the integration of a multi-stimuli responsive gate dielectric and semiconductor channel into the single field-effect transistor (FET) platform.
View details for DOI 10.1002/adma.201302869
View details for PubMedID 24493054
- 25th Anniversary Article: The Evolution of Electronic Skin (E-Skin): A Brief History, Design Considerations, and Recent Progress ADVANCED MATERIALS 2013; 25 (42): 5997-6037
A rapid and efficient self-healing thermo-reversible elastomer crosslinked with graphene oxide.
2013; 25 (40): 5785-5790
A self-healing thermo-reversible elastomer is synthesized by cross-linking a hydrogen bonding polymer network with chemically-modified graphene oxide. This nanocomposite allows for both rapid and efficient self-healing (in only several minutes) at room temperature, without the need for any external stimuli (e.g., heating or light exposure), healing agents, plasticizers or solvents.
View details for DOI 10.1002/adma.201302962
View details for PubMedID 23946261
- STRETCHABLE LEDS Light-emitting electronic skin NATURE PHOTONICS 2013; 7 (10): 769-771
Investigation of protein detection parameters using nanofunctionalized organic field-effect transistors.
2013; 7 (5): 3970-3980
Biodetection using organic field-effect transistors (OFETs) is gaining increasing interest for applications as diverse as food security, environmental monitoring, and medical diagnostics. However, there still lacks a comprehensive, empirical study on the fundamental limits of OFET sensors. In this paper, we present a thorough study of the various parameters affecting biosensing using an OFET decorated with gold nanoparticle (AuNP) binding sites. These parameters include the spacing between receptors, pH of the buffer, and ionic strength of the buffer. To this end, we employed the thrombin protein and its corresponding DNA binding aptamer to form our model detection system. We demonstrate a detection limit of 100 pM for this protein with high selectivity over other proteases in situ. We describe herein a feasible approach for protein detection with OFETs and a thorough investigation of parameters governing biodetection events using OFETs. Our obtained results should provide important guidelines to tailor the sensor's dynamic range to suit other desired OFET-based biodetection applications.
View details for DOI 10.1021/nn305903q
View details for PubMedID 23597051
Transparent, Optical, Pressure-Sensitive Artificial Skin for Large-Area Stretchable Electronics
2012; 24 (24): 3223-3227
Optical pressure sensors are highly responsive and are unaffected by surrounding parameters such as electronic noise, humidity, temperature, etc. A new type of optical pressure sensor is described that demonstrates the stretchability and transparency of a polydimethylsiloxane waveguide, while also serving as a substrate. The pressure sensors are both robust and easy to fabricate over a large area.
View details for DOI 10.1002/adma.201200523
View details for Web of Science ID 000305450500009
View details for PubMedID 22641411
Chemical and Engineering Approaches To Enable Organic Field-Effect Transistors for Electronic Skin Applications
ACCOUNTS OF CHEMICAL RESEARCH
2012; 45 (3): 361-371
Skin is the body's largest organ and is responsible for the transduction of a vast amount of information. This conformable material simultaneously collects signals from external stimuli that translate into information such as pressure, pain, and temperature. The development of an electronic material, inspired by the complexity of this organ is a tremendous, unrealized engineering challenge. However, the advent of carbon-based electronics may offer a potential solution to this long-standing problem. In this Account, we describe the use of an organic field-effect transistor (OFET) architecture to transduce mechanical and chemical stimuli into electrical signals. In developing this mimic of human skin, we thought of the sensory elements of the OFET as analogous to the various layers and constituents of skin. In this fashion, each layer of the OFET can be optimized to carry out a specific recognition function. The separation of multimodal sensing among the components of the OFET may be considered a "divide and conquer" approach, where the electronic skin (e-skin) can take advantage of the optimized chemistry and materials properties of each layer. This design of a novel microstructured gate dielectric has led to unprecedented sensitivity for tactile pressure events. Typically, pressure-sensitive components within electronic configurations have suffered from a lack of sensitivity or long mechanical relaxation times often associated with elastomeric materials. Within our method, these components are directly compatible with OFETs and have achieved the highest reported sensitivity to date. Moreover, the tactile sensors operate on a time scale comparable with human skin, making them ideal candidates for integration as synthetic skin devices. The methodology is compatible with large-scale fabrication and employs simple, commercially available elastomers. The design of materials within the semiconductor layer has led to the incorporation of selectivity and sensitivity within gas-sensing devices and has enabled stable sensor operation within aqueous media. Furthermore, careful tuning of the chemical composition of the dielectric layer has provided a means to operate the sensor in real time within an aqueous environment and without the need for encapsulation layers. The integration of such devices as electronic mimics of skin will require the incorporation of biocompatible or biodegradable components. Toward this goal, OFETs may be fabricated with >99% biodegradable components by weight, and the devices are robust and stable, even in aqueous environments. Collectively, progress to date suggests that OFETs may be integrated within a single substrate to function as an electronic mimic of human skin, which could enable a large range of sensing-related applications from novel prosthetics to robotic surgery.
View details for DOI 10.1021/ar2001233
View details for Web of Science ID 000302033000005
View details for PubMedID 21995646
Selective dispersion of high purity semiconducting single-walled carbon nanotubes with regioregular poly(3-alkylthiophene)s
Conjugated polymers, such as polyfluorene and poly(phenylene vinylene), have been used to selectively disperse semiconducting single-walled carbon nanotubes (sc-SWNTs), but these polymers have limited applications in transistors and solar cells. Regioregular poly(3-alkylthiophene)s (rr-P3ATs) are the most widely used materials for organic electronics and have been observed to wrap around SWNTs. However, no sorting of sc-SWNTs has been achieved before. Here we report the application of rr-P3ATs to sort sc-SWNTs. Through rational selection of polymers, solvent and temperature, we achieved highly selective dispersion of sc-SWNTs. Our approach enables direct film preparation after a simple centrifugation step. Using the sorted sc-SWNTs, we fabricate high-performance SWNT network transistors with observed charge-carrier mobility as high as 12 cm(2) V(-1) s(-1) and on/off ratio of >10(6). Our method offers a facile and a scalable route for separating sc-SWNTs and fabrication of electronic devices.
View details for DOI 10.1038/ncomms1545
View details for Web of Science ID 000297686500028
View details for PubMedID 22086341
Syntheses of Organic Molecule-DNA Hybrid Structures
2011; 5 (3): 2067-2074
Investigation of robust and efficient pathways to build DNA-organic molecule hybrid structures is fundamentally important to realize controlled placement of single molecules for potential applications, such as single-molecule electronic devices. Herein, we report a systematic investigation of synthetic processes for preparing organic molecule-DNA building blocks and their subsequent elongation to generate precise micrometer-sized structures. Specifically, optimal cross-coupling routes were identified to enable chemical linkages between three different organic molecules, namely, polyethylene glycol (PEG), poly(p-phenylene ethynylene) (PPE), and benzenetricarboxylate, with single-stranded (ss) DNA. The resulting DNA-organic molecule hybrid building blocks were purified and characterized by both denaturing gel electrophoresis and electrospray ionization mass spectrometry (ESI-MS). The building blocks were subsequently elongated through both the DNA hybridization and ligation processes to prepare micrometer-sized double-stranded (ds) DNA-organic molecule hybrid structures. The described synthetic procedures should facilitate future syntheses of various hybrid DNA-based organic molecular structures.
View details for DOI 10.1021/nn1032455
View details for Web of Science ID 000288570600062
View details for PubMedID 21323343
Aptamer-Based SERRS Sensor for Thrombin Detection
2008; 8 (12): 4386-4390
We describe an aptamer-based surface enhanced resonance Raman scattering (SERRS) sensor with high sensitivity, specificity, and stability for the detection of a coagulation protein, human alpha-thrombin. The sensor achieves high sensitivity and a limit of detection of 100 pM by monitoring the SERRS signal change upon the single-step of thrombin binding to immobilized thrombin binding aptamer. The selectivity of the sensor is demonstrated by the specific discrimination of thrombin from other protein analytes. The specific recognition and binding of thrombin by the thrombin binding aptamer is essential to the mechanism of the aptamer-based sensor, as shown through measurements using negative control oligonucleotides. In addition, the sensor can detect 1 nM thrombin in the presence of complex biofluids, such as 10% fetal calf serum, demonstrating that the immobilized, 5'-capped, 3'-capped aptamer is sufficiently robust for clinical diagnostic applications. Furthermore, the proposed sensor may be implemented for multiplexed detection using different aptamer-Raman probe complexes.
View details for DOI 10.1021/nl802245w
View details for Web of Science ID 000261630700052
View details for PubMedID 19367849
- Sensitive and selective viral DNA detection assay via microbead-based rolling circle amplification BIOORGANIC & MEDICINAL CHEMISTRY LETTERS 2008; 18 (22): 5871-5874
Synthesis of DNA-organic molecule-DNA triblock oligomers using the amide coupling reaction and their enzymatic amplification
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2008; 130 (39): 12854-?
Precise electrical contact between single-molecule and electrodes is a first step to study single-molecule electronics and its application such as (bio)sensors and nanodevices. To realize a reliable electrical contact, we can use DNA as a template in the field of nanoelectronics because of its micrometer-scaled length with the thickness of nanometer-scale. In this paper, we studied the reactivity of the amide-coupling reaction to tether oligodeoxynucleotides (ODNs) to organic molecules and the elongation of the ODNs by the polymerase chain reaction (PCR) to synthesize 1.5 kbp dsDNA-organic molecule-1.5 kbp dsDNA (DOD) triblock architecture. The successful amide-coupling reactions were confirmed by electrospray ionization mass spectrometry (ESI-MS), and the triblock architectures were characterized by 1% agarose gel electrophoresis and atomic force microscope (AFM). Our result shows that this strategy is simple and makes it easy to construct DNA-organic molecule-DNA triblock architectures and potentially provides a platform to prepare and investigate single molecule electronics.
View details for DOI 10.1021/ja8044458
View details for Web of Science ID 000259553700009
View details for PubMedID 18763775
Massively Parallel Interrogation of Aptamer Sequence, Structure and Function
2008; 3 (7)
Optimization of high affinity reagents is a significant bottleneck in medicine and the life sciences. The ability to synthetically create thousands of permutations of a lead high-affinity reagent and survey the properties of individual permutations in parallel could potentially relieve this bottleneck. Aptamers are single stranded oligonucleotides affinity reagents isolated by in vitro selection processes and as a class have been shown to bind a wide variety of target molecules.High density DNA microarray technology was used to synthesize, in situ, arrays of approximately 3,900 aptamer sequence permutations in triplicate. These sequences were interrogated on-chip for their ability to bind the fluorescently-labeled cognate target, immunoglobulin E, resulting in the parallel execution of thousands of experiments. Fluorescence intensity at each array feature was well resolved and shown to be a function of the sequence present. The data demonstrated high intra- and inter-chip correlation between the same features as well as among the sequence triplicates within a single array. Consistent with aptamer mediated IgE binding, fluorescence intensity correlated strongly with specific aptamer sequences and the concentration of IgE applied to the array.The massively parallel sequence-function analyses provided by this approach confirmed the importance of a consensus sequence found in all 21 of the original IgE aptamer sequences and support a common stem:loop structure as being the secondary structure underlying IgE binding. The microarray application, data and results presented illustrate an efficient, high information content approach to optimizing aptamer function. It also provides a foundation from which to better understand and manipulate this important class of high affinity biomolecules.
View details for DOI 10.1371/journal.pone.0002720
View details for Web of Science ID 000264057200058
View details for PubMedID 18628955
- Single microbead SELEX for efficient ssDNA aptamer generation against botulinum neurotoxin CHEMICAL COMMUNICATIONS 2008: 1883-1885
Biofunctional subwavelength optical waveguides for biodetection
2008; 2 (2): 255-262
We report a versatile biofunctional subwavelength photonic device platform for real-time detection of biological molecules. Our devices contain lipid bilayer membranes fused onto metal oxide nanowire waveguides stretched across polymeric flow channels. The lipid bilayers incorporating target receptors are submersed in the propagating evanescent field of the optical cavity. We show that the lipid bilayers in our devices are continuous, have very high mobile fraction, and are resistant to fouling. We also demonstrate that our platform allows rapid membrane exchange. Finally, we use this device to detect the hybridization of specific DNA target sequences in solution to complementary probe DNA strands anchored to the lipid bilayer. This evanescent wave sensing architecture holds great potential for portable, all-optical detection systems.
View details for DOI 10.1021/nn700220b
View details for Web of Science ID 000253503300014
View details for PubMedID 19206625
Protein detection via direct enzymatic amplification of short DNA aptamers
2008; 373 (1): 121-128
Aptamers are single-stranded nucleic acids that fold into defined tertiary structures to bind target molecules with high specificities and affinities. DNA aptamers have garnered much interest as recognition elements for biodetection and diagnostic applications due to their small size, ease of discovery and synthesis, and chemical and thermal stability. Here we describe the design and application of a short DNA molecule capable of both protein target binding and amplifiable bioreadout processes. Because both recognition and readout capabilities are incorporated into a single DNA molecule, tedious conjugation procedures required for protein-DNA hybrids can be omitted. The DNA aptamer is designed to be amplified directly by either polymerase chain reaction (PCR) or rolling circle amplification (RCA) processes, taking advantage of real-time amplification monitoring techniques for target detection. A combination of both RCA and PCR provides a wide protein target dynamic range (1 microM to 10 pM).
View details for DOI 10.1016/j.ab.2007.09.035
View details for Web of Science ID 000252069000015
View details for PubMedID 17980857
Aptasensors for biosecurity applications
CURRENT OPINION IN CHEMICAL BIOLOGY
2007; 11 (3): 316-328
Nucleic acid (aptasensors) have found steadily increased utility and application over the past decade. In particular, aptamers have been touted as a valuable complement to and, in some cases, replacement for antibodies owing to their structural and functional robustness as well as their ease in generation and synthesis. They are thus attractive for biosecurity applications (e.g. pathogen detection) and are especially well suited because their in vitro generation process does not require infection of any host systems. Herein we provide a brief overview of the aptamers generated against pathogens and toxins over the past few years. In addition, a few recently described detection platforms using aptamers and potentially suitable applications for biosecurity will be discussed.
View details for DOI 10.1016/j.cbpa.2007.05.017
View details for Web of Science ID 000248143600011
View details for PubMedID 17548236
Heightened sense for sensing: recent advances in pathogen immunoassay sensing platforms
2007; 132 (3): 187-191
Rapid and efficient sensors are essential for effective defense against the emerging threat of bioterrorism and biological warfare. This review article describes several recent immunosensing advances that are relevant to biothreat detection. These highly diverse examples are intended to demonstrate the breadth of these immunochemical sensing systems and platforms while highlighting those technologies that are suitable for pathogen detection.
View details for DOI 10.1039/b615477h
View details for Web of Science ID 000244487700001
View details for PubMedID 17325749
- Assembly and alignment of metallic nanorods on surfaces with patterned wettability SMALL 2006; 2 (12): 1448-1453
Generating short peptidic ligands for silver nanowires from phage display random libraries
BIOORGANIC & MEDICINAL CHEMISTRY LETTERS
2006; 16 (20): 5261-5264
We report the generation of peptide ligands for silver nanowires using a linear 12-mer peptide phage display random library technique. Phage clones that specifically bind the silver nanowires are sequenced after three rounds of biopanning, and obtained DNA sequences suggest that there are a few conserved amino acid residues which may be critical for binding. A selected binding peptide, together with two mutant peptide sequences, were subsequently synthesized on Tentagel resins to examine the importance of both the identities and positions of the conserved amino acid residues.
View details for DOI 10.1016/j.bmcl.2006.08.013
View details for Web of Science ID 000241344400001
View details for PubMedID 16934463
Dual-acting agents that possess free radical scavenging and antithrombotic activities: Design, synthesis, and evaluation of phenolic tetrahydro-beta-carboline RGD peptide conjugates
BIOORGANIC & MEDICINAL CHEMISTRY LETTERS
2006; 16 (17): 4523-4527
A new approach to construct a single dual-acting agent is described. Compounds 6a-c are potent free radical scavengers as demonstrated by the EC(50) values in PC12 cell survival assay in term of NO, H(2)O(2), and ()OH scavenging activity. The Ach-induced vaso-relaxation assay further confirms the potent NO scavenging activity of compounds 6a-c. In addition, 6a-c are efficacious in a rat arterial thrombosis, and are active in ADP- or PAF-induced in vitro platelet aggregation assay, suggesting that compounds 6a-c also possess anti-thrombotic activities. Since both free radical and thrombogenesis are important risk factors in myocardial ischemic/reperfusion injuries, these dual-acting agents having both free radical scavenging and antithrombolic activities may potentially be beneficial toward their treatment.
View details for DOI 10.1016/j.bmcl.2006.06.024
View details for Web of Science ID 000240056000017
View details for PubMedID 16797986
- Metallic striped nanowires as multiplexed immunoassay platforms for pathogen detection ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 2006; 45 (41): 6900-6904