Onur Parlak is a postdoctoral research fellow at Stanford University, Materials Science and Engineering, working with Prof. Alberto Salleo. He received his PhD degree in Bioelectronics from Linköping University, Biosensors and Bioelectronics Centre, Sweden in September 2015. Earlier, he was visiting research intern at Nanyang Technological University, Materials Science and Engineering Department, Singapore in 2011. He received his master and bachelor degree from Izmir Institute of Technology, Department of Chemistry in 2011 and 2009, respectively. He was recently awarded by one of the most prestigious grant in Sweden, Knut Allice Wallenberg Foundation for postdoctoral research at Stanford. .
Dr. Parlak’s research in Stanford University focuses on wearable biosensors for early diagnosis of metabolic diesease, energy storage materials for biosensing devices and interfacing various nanomaterials for bioelectronics.
Honors & Awards
Postdoctoral Scholarship, Knut Allice Wallenberg Foundation (2015)
Doctor of Philosophy, Linkoping University (2015)
Master of Science, Izmir Institute of Technology, Chemistry (2011)
Bachelor of Science, Izmir Institute of Technology, Chemistry (2009)
Alberto Salleo, Postdoctoral Faculty Sponsor
Current Research and Scholarly Interests
One of the most important and recent trend in biosensor technology is continuous monitoring of metabolite using wearable biosensors. In parallel to the advancement in wearable electronics, wearable sensor-based systems for healthcare applications have attracted a significant interest both in industrial and academic research. Wearable biosensor applications aim to change centralised hospital-based care system to home-based personal medicine, and reduce healthcare cost and time for diagnosis. Electrochemical transducers offer many advantages for wearable sensors for physiological monitoring, and can be easily integrated onto textile materials or directly on the skin.
Early research activities on wearable health monitoring have mainly focused on addressing the demand of physical sensing. These efforts have resulted in successful wearable physical sensors, such as temperature and pressure, for monitoring biophysical signals including heart rate, respiration rate, skin temperature, and brain activity.However, these physical sensors require external complementary measures to diagnose diseases precisely. On the other hand, wearable biosensors are able to give direct information about specific disease biomarkers and metabolite changes in bodily fluids. Our research focus is to develop wearable biosensing devices for specific disease biomarkers for continous helath monitoring.
Molecularly selective nanoporous membrane-based wearable organic electrochemical device for noninvasive cortisol sensing.
2018; 4 (7): eaar2904
Wearable biosensors have emerged as an alternative evolutionary development in the field of healthcare technology due to their potential to change conventional medical diagnostics and health monitoring. However, a number of critical technological challenges including selectivity, stability of (bio)recognition, efficient sample handling, invasiveness, and mechanical compliance to increase user comfort must still be overcome to successfully bring devices closer to commercial applications. We introduce the integration of an electrochemical transistor and a tailor-made synthetic and biomimetic polymeric membrane, which acts as a molecular memory layer facilitating the stable and selective molecular recognition of the human stress hormone cortisol. The sensor and a laser-patterned microcapillary channel array are integrated in a wearable sweat diagnostics platform, providing accurate sweat acquisition and precise sample delivery to the sensor interface. The integrated devices were successfully used with both ex situ methods using skin-like microfluidics and on human subjects with on-body real-sample analysis using a wearable sensor assembly.
View details for DOI 10.1126/sciadv.aar2904
View details for PubMedID 30035216
- Organic Electronics for Point-of-Care Metabolite Monitoring TRENDS IN BIOTECHNOLOGY 2018; 36 (1): 45–59
- Hierarchical Aerographite nano-microtubular tetrapodal networks based electrodes as lightweight supercapacitor NANO ENERGY 2017; 34: 570-577
Structuring Au nanoparticles on two-dimensional MoS2 nanosheets for electrochemical glucose biosensors
BIOSENSORS & BIOELECTRONICS
2017; 89: 545-550
Two-dimensional (2D) bioelectronics is an emerging field of research which fuses the advantages of 2D nanomaterials with those of nanobiotechnology. Due to the various physical and chemical properties present in layered counterparts of 2D materials, including high charge density, large surface area, remarkable electron mobility, ready electron transport, sizeable band gaps and ease of hybridisation, they are set to become a versatile tool to fabricate sensitive and selective novel biodevices, which might offer an unique advantages to tackle key energy, medical and environmental issues. Current 2D bioelectronics research is focused on the design of simple-to-use and cheaper biodevices, while improving their selectivity, sensitivity and stability. However, current designs generally suffer from a lack of efficiency, relatively low sensitivity, slow electron transfer kinetics, high background charging current and low current density arising from poor mass transport. Here, we report a nanoparticle-structured MoS2 nanosheet as an ideal semiconductor interface, which is able to form a homogenous layer on the electrode surface for the assembly of gold nanoparticles. This not only enhances electrocatalytic reactions, but also provides excellent electrochemical properties such as high faradic-to-capacitive current ratios, high current density and electron mobility, and faster mass transport, due to the dominance of radial diffusion. The MoS2/Au NPs/GOx bioelectrode exhibits a linear response to glucose from 0.25 to 13.2mM, with a detection limit of 0.042µM (S/N=3) and sensitivity of 13.80µA/µM/cm2.
View details for DOI 10.1016/j.bios.2016.03.024
View details for Web of Science ID 000391077000055
Acetylene-sourced CVD-synthesised catalytically active graphene for electrochemical biosensing
BIOSENSORS & BIOELECTRONICS
2017; 89: 496-504
In this study, we have demonstrated the use of chemical vapour deposition (CVD) grown-graphene to develop a highly-ordered graphene-enzyme electrode for electrochemical biosensing. The graphene sheets were deposited on 1.00mm thick copper sheet at 850°C using acetylene (C2H2) as carbon source in an argon (Ar) and nitrogen (N2) atmosphere. An anionic surfactant was used to increase wettability and hydrophilicity of graphene; thereby facilitating the assembly of biomolecules on the electrode surface. Meanwhile, the theoretical calculations confirmed the successful modification of hydrophobic nature of graphene through the anionic surface assembly, which allowed high-ordered immobilisation of glucose oxidase (GOx) on the graphene. The electrochemical sensing activities of the graphene-electrode was explored as a model for bioelectrocatalysis. The bioelectrode exhibited a linear response to glucose concentration ranging from 0.2 to 9.8mM, with sensitivity of 0.087µA/µM/cm(2) and a detection limit of 0.12µM (S/N=3). This work sets the stage for the use of acetylene-sourced CVD-grown graphene as a fundamental building block in the fabrication of electrochemical biosensors and other bioelectronic devices.
View details for DOI 10.1016/j.bios.2016.03.063
View details for Web of Science ID 000391077000048
View details for PubMedID 27157880
Bioinspired design of a polymer-based biohybrid sensor interface
Sensors and Actuators B: Chemical
View details for DOI 10.1016/j.snb.2017.05.030
Interfacing Graphene for Electrochemical Biosensing
Materials for Chemical Sensing
Springer International Publishing. 2017: 105–122
View details for DOI 10.1007/978-3-319-47835-7_5
BIOSENSORS & BIOELECTRONICS
2016; 76: 251-265
We review the rapidly emerging field of switchable interfaces and its implications for bioelectronics. We seek to piece together early breakthroughs and key developments, and highlight and discuss the future of switchable bioelectronics by focusing on bio-electrochemical processes based on mimicking and controlling biological environments with external stimuli. All these studies strive to answer a fundamental question: "how do living systems probe and respond to their surroundings? And, following on from that: "how one can transform these concepts to serve the practical world of bioelectronics?" The central obstacle to this vision is the absence of versatile interfaces that are able to control and regulate the means of communication between biological and electronic systems. Here, we review the overall progress made to date in building such interfaces at the level of individual biomolecules and focus on the latest efforts to generate device platforms that integrate bio-interfaces with electronics.
View details for DOI 10.1016/j.bios.2015.06.023
View details for Web of Science ID 000364895000020
View details for PubMedID 26139319
Light-Triggered Switchable Graphene–Polymer Hybrid Bioelectronics
Advanced Materials Interfaces
2016; 3: 1500353
View details for DOI 10.1002/admi.201500353
Programmable bioelectronics in a stimuli-encoded 3D graphene interface
2016; 8 (19): 9976-9981
The ability to program and mimic the dynamic microenvironment of living organisms is a crucial step towards the engineering of advanced bioelectronics. Here, we report for the first time a design for programmable bioelectronics, with 'built-in' switchable and tunable bio-catalytic performance that responds simultaneously to appropriate stimuli. The designed bio-electrodes comprise light and temperature responsive compartments, which allow the building of Boolean logic gates (i.e."OR" and "AND") based on enzymatic communications to deliver logic operations.
View details for DOI 10.1039/c6nr02355j
View details for Web of Science ID 000376047200005
View details for PubMedID 27121984
Null Extinction of Ceria@silica Hybrid Particles: Transparent Polystyrene Composites
ACS APPLIED MATERIALS & INTERFACES
2015; 7 (49): 27539-27546
Scattering of light in optical materials, particularly in composites based on transparent polymer and inorganic pigment nanoparticles, is a chronic problem. It might originate mainly from light scattering because of a refractive index mismatch between the particles and transparent polymer matrix. Thus, the intensity of light is rapidly diminished and optical transparency is reduced. Refractive index matching between the pigment core and the surrounding transparent matrix using a secondary component at the interface (shell) has recently appeared as a promising approach to alter light scattering. Here, CeO2 (ceria) nanoparticles with a diameter of 25 nm are coated with a SiO2 (silica) shell with various thicknesses in a range of 6.5-67.5 nm using the Stöber method. When the hybrid core-shell particles are dispersed into transparent polystyrene (PS), the transmission of the freestanding PS composite films increases over both the ultraviolet (UV) and visible region as the shell thickness increases particularly at 37.5 nm. The increase of transmission can be attributed to the reduction in the scattering coefficient of the hybrid particles. On the other hand, the particles in tetrahydrofuran (THF) absorb over UV and the intensity of absorption shows a systematic decrease as the shell thickness increases. Thus, the silica shell suppresses not only the scattering coefficient but also the molar absorptivity of the core ceria particles. The experimental results regarding the target shell thickness to develop low extinction (scattering + absorption) composites show a qualitative agreement with the predictions of Effective Medium Theory.
View details for DOI 10.1021/acsami.5b09818
View details for Web of Science ID 000366873900061
View details for PubMedID 26594909
Switchable Bioelectrocatalysis Controlled by Dual Stimuli-Responsive Polymeric Interface
ACS APPLIED MATERIALS & INTERFACES
2015; 7 (43): 23837-23847
The engineering of bionanointerfaces using stimuli-responsive polymers offers a new dimension in the design of novel bioelectronic interfaces. The integration of electrode surfaces with stimuli-responsive molecular cues provides a direct control and ability to switch and tune physical and chemical properties of bioelectronic interfaces in various biodevices. Here, we report a dual-responsive biointerface employing a positively responding dual-switchable polymer, poly(NIPAAm-co-DEAEMA)-b-HEAAm, to control and regulate enzyme-based bioelectrocatalysis. The design interface exhibits reversible activation-deactivation of bioelectrocatalytic reactions in response to change in temperature and in pH, which allows manipulation of biomolecular interactions to produce on/off switchable conditions. Using electrochemical measurements, we demonstrate that interfacial bioelectrochemical properties can be tuned over a modest range of temperature (i.e., 20-60 °C) and pH (i.e., pH 4-8) of the medium. The resulting dual-switchable interface may have important implications not only for the design of responsive biocatalysis and on-demand operation of biosensors, but also as an aid to elucidating electron-transport pathways and mechanisms in living organisms by mimicking the dynamic properties of complex biological environments and processes.
View details for DOI 10.1021/acsami.5b06048
View details for Web of Science ID 000364355500004
View details for PubMedID 26440202
- Switchable bioelectronics on graphene interface BIOSENSING AND NANOMEDICINE VIII 2015; 9550
Advanced Synthetic Materials in Detection Science, Subrayal Reddy (Ed.). (2014)
Biosensors and Bioelectronics
2015; 68: 41
View details for DOI 10.1016/j.bios.2014.12.038
- pH-induced on/off-switchable graphene bioelectronics JOURNAL OF MATERIALS CHEMISTRY B 2015; 3 (37): 7434-7439
- Two-Dimensional Gold-Tungsten Disulphide Bio-Interface for High-Throughput Electrocatalytic Nano-Bioreactors ADVANCED MATERIALS INTERFACES 2014; 1 (6)
- Self-Reporting Micellar Polymer Nanostructures for Optical Urea Biosensing INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH 2014; 53 (20): 8509-8514
On/Off-Switchable Zipper-Like Bioelectronics on a Graphene Interface
2014; 26 (3): 482-486
An on/off-switchable graphene-based zipper-like interface is architectured for efficient bioelectrocatalysis. The graphene interface transduces a temperature input signal into structural changes of the membrane, resulting in the amplification of electrochemical signals and their transformation into the gated transport of molecules through the membrane.
View details for DOI 10.1002/adma.201303075
View details for Web of Science ID 000334289300015
View details for PubMedID 24142541
Template-directed hierarchical self-assembly of graphene based hybrid structure for electrochemical biosensing
BIOSENSORS & BIOELECTRONICS
2013; 49: 53-62
A template-directed self-assembly approach, using functionalised graphene as a fundamental building block to obtain a hierarchically ordered graphene-enzyme-nanoparticle bioelectrode for electrochemical biosensing, is reported. An anionic surfactant was used to prepare a responsive, functional interface and direct the assembly on the surface of the graphene template. The surfactant molecules altered the electrostatic charges of graphene, thereby providing a convenient template-directed assembly approach to a free-standing planar sheet of sp(2) carbons. Cholesterol oxidase and cholesterol esterase were assembled on the surface of graphene by intermolecular attractive forces while gold nanoparticles are incorporated into the hetero-assembly to enhance the electro-bio-catalytic activity. Hydrogen peroxide and cholesterol were used as two representative analytes to demonstrate the electrochemical sensing performance of the graphene-based hybrid structure. The bioelectrode exhibited a linear response to H2O2 from 0.01 to 14 mM, with a detection limit of 25 nM (S/N=3). The amperometric response with cholesterol had a linear range from 0.05 to 0.35 mM, sensitivity of 3.14 µA/µM/cm(2) and a detection limit of 0.05 µM. The apparent Michaelis-Menten constant (Km(app)) was calculated to be 1.22 mM. This promising approach provides a novel methodology for template-directed bio-self-assembly over planar sp(2) carbons of a graphene sheet and furnishes the basis for fabrication of ultra-sensitive and efficient electrochemical biosensors.
View details for DOI 10.1016/j.bios.2013.04.004
View details for Web of Science ID 000323396700009
View details for PubMedID 23708818
- Anomalous transmittance of polystyrene-ceria nanocomposites at high particle loadings JOURNAL OF MATERIALS CHEMISTRY C 2013; 1 (2): 290-298
- Synthesis of amidoximated polyacrylonitrile fibers and its application for sorption of aqueous uranyl ions under continuous flow CHEMICAL ENGINEERING JOURNAL 2012; 213: 41-49
Toward Transparent Nanocomposites Based on Polystyrene Matrix and PMMA-Grafted CeO2 Nanoparticles
ACS APPLIED MATERIALS & INTERFACES
2011; 3 (11): 4306-4314
The association of transparent polymer and nanosized pigment particles offers attractive optical materials for various potential and existing applications. However, the particles embedded into polymers scatter light due to refractive index (RI) mismatch and reduce transparency of the resulting composite material. In this study, optical composites based on polystyrene (PS) matrix and poly(methyl methacrylate) (PMMA)-grafted CeO(2) hybrid particles were prepared. CeO(2) nanoparticles with an average diameter of 18 ± 8 nm were precipitated by treating Ce(NO(3))·6H(2)O with urea in the presence of a polymerizable surfactant, 3-methacyloxypropyltrimethoxy silane. PMMA chains were grafted on the surface of the nanoparticles upon free radical in situ solution polymerization. While blending of unmodified CeO(2) particles with PS resulted in opaque films, the transparency of the composite films was remarkably enhanced when prepared by PMMA-grafted CeO(2) hybrid particles, particularly those having a PMMA thickness of 9 nm. The improvement in transparency is presumably due to the reduction in RI mismatch between CeO(2) particles and the PS matrix when using PMMA chains at the interface.
View details for DOI 10.1021/am200983h
View details for Web of Science ID 000297195500022
View details for PubMedID 21970464