Nanohybrids of graphene and two-dimensional (2D) layered transition metal dichalcogenides (TMD) nanostructures can provide a promising substrate for extraordinary surface-enhanced Raman spectroscopy (SERS) due to the combined electromagnetic enhancement on TMD nanostructures via localized surface plasmonic resonance (LSPR) and chemical enhancement on graphene. In these nanohybrid SERS substrates, the LSPR on TMD nanostructures is affected by the TMD morphology. Herein, we report the first successful growth of MoS2 nanodonuts (N-donuts) on graphene using a vapor transport process on graphene. Using Rhodamine 6G (R6G) as a probe, SERS spectra were compared on MoS2 N-donuts/graphene nanohybrids substrates. A remarkably high R6G SERS sensitivity up to 2 × 10−12 M has been obtained, which can be attributed to the more robust LSPR effect than in other TMD nanostructures such as nanodiscs as suggested by the finite-difference time-domain simulation. This result demonstrates that non-metallic TMD/graphene nanohybrids substrates can have SERS sensitivity up to one order of magnitude higher than that reported on the plasmonic metal nanostructures/2D materials SERS substrates, providing a promising scheme for high-sensitivity, low-cost applications for biosensing.
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Cation–π Interaction Assisted Molecule Attachment and Photocarrier Transfer in Rhodamine/Graphene Heterostructures
Cation–π interactions between molecules and graphene are known to have a profound effect on the properties of the molecule/graphene nanohybrids and motivate this study to quantify the attachment of the rhodamine 6G (R6G) dye molecules on graphene and the photocarrier transfer channel formed across the R6G/graphene interface. By increasing the R6G areal density of the R6G on graphene field‐effect transistor (GFET) from 0 up to ≈3.6 × 1013cm−2, a linear shift of the Dirac point of the graphene from originally 1.2 V (p‐doped) to −1 V (n‐doped) is revealed with increasing number of R6G molecules. This indicates that the attachment of the R6G molecules on graphene is determined by the cation–π interaction between the NH+ in R6G and π electrons in graphene. Furthermore, a linear dependence of the photoresponse on the R6G molecule concentration to 550 nm illumination is observed on the R6G/graphene nanohybrid, suggesting that the cation–π interaction controls the R6G attachment configuration to graphene to allow formation of identical photocarrier transfer channels. On R6G/graphene nanohybrid with 7.2 × 107R6G molecules, high responsivity up to 5.15 × 102A W−1is obtained, suggesting molecule/graphene nanohybrids are promising for high‐performance optoelectronics.
more » « less- NSF-PAR ID:
- 10451038
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials Interfaces
- Volume:
- 7
- Issue:
- 16
- ISSN:
- 2196-7350
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Biomolecule/graphene van der Waals heterojunction provides a generic platform for designing high‐performance, flexible, and scalable optoelectronics. A key challenge is, in controllable attachment, the biomolecules to form a desired interfacial electronic structure for a high‐efficiency optoelectronic process of photoabsorption, exciton dissociation into photocarriers, carrier transfer, and transport. Here, it is shown that a polarity‐controlled attachment of the Cytochrome c (Cyt c) biomolecules can be achieved on the channel of graphene field effect transistors (GFET). High‐efficiency charge transfer across the formed Cyt c/graphene interface is demonstrated when Cyt c attaches with positively charged side to GFET as predicted by molecular dynamics simulation and confirmed experimentally. This Cyt c/GFET van der Waals heterojunction nanohybrid photodetector exhibits a spectral photoresponsivity resembling the absorption spectrum of the Cyt c, confirming the role of Cty c as the photosensitizer in the device. The high visible photoresponsivity up to 7.57 × 104A W−1can be attributed to the high photoconductive gain in exceeding 105facilitated by the high carrier mobility in graphene. This result therefore demonstrates a viable approach in synthesis of the biomolecule/graphene van der Waals heterojunction optoelectronics using polarity‐controlled biomolecule attachment, which can be expanded for on‐chip printing of high‐performance molecular optoelectronics.
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Nanohybrids represent a larger variety of functional materials consisting of one or more types of low‐dimensional semiconductor nanostructures, such as quantum dots, nanowires, nanotubes, 2D atomic materials (graphene, transition‐metal dichalcogenides, etc.) interfaced with one another, and/or with conventional material matrices (bulks, films, polymers, etc.). Heterojunction interfaces are characteristic in nanohybrids and play a critical role facilitating synergistic coupling of constituent materials of different functionalities, resulting in excellent electronic, optoelectronic, and mechanical properties. Therefore, nanohybrids provide fresh opportunities for designs of optoelectronic devices of extraordinary performance in addition to the benefits of low cost, large abundance, flexibility, and light weight. Herein, some recent achievements in exploiting new optoelectronic nanohybrids and understanding the underlying physics toward high‐performance optoelectronic nanohybrids that are competitive in commercialization of various optoelectronic devices are highlighted. Using nanohybrid photodetectors as an example, the importance in controlling the heterojunction interfaces and multiscale controlling of optoelectronic process of light absorption, exciton dissociation, photocarrier transfer, and transport from atomic to device scales and how this control impacts the photodetector performance are revealed. The current status, remaining challenges, and future perspectives in optoelectronic nanohybrids are also discussed.
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Abstract Two‐dimensional transition metal dichalcogenides (TMDs)/graphene van der Waals (vdW) heterostructures integrate the superior light–solid interaction in TMDs and charge mobility in graphene, and therefore are promising for surface‐enhanced Raman spectroscopy (SERS). Herein, a novel TMD (MoS2and WS2) nanodome/graphene vdW heterostructure SERS substrate, on which an extraordinary SERS sensitivity is achieved, is reported. Using fluorescent Rhodamine 6G (R6G) as probe molecules, the SERS sensitivity is in the range of 10−11to 10−12
m on the TMD nanodomes/graphene vdW heterostructure substrates using 532 nm Raman excitation, which is comparable to the best sensitivity reported so far using plasmonic metal nanostructures/graphene SERS substrates, and is more than three orders of magnitude higher than that on single‐layer TMD and graphene substrates. Density functional theory simulation reveals enhanced electric dipole moments and dipole–dipole interaction at the TMD/graphene vdW interface, yielding an effective means to facilitate an external electrostatic perturbation on the graphene surface and charge transfer. This not only promotes chemical enhancement on SERS, but also enables electromagnetic enhancement of SERS through the excitation of localized surface plasmonic resonance on the TMD nanodomes. This TMD nanodome/graphene vdW heterostructure is therefore promising for commercial applications in high‐performance optoelectronics and sensing. -
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Neurotransmitters are small molecules involved in neuronal signaling and can also serve as stress biomarkers.1Their abnormal levels have been also proposed to be indicative of several neurological diseases such as Alzheimer’s disease, Parkinson’s disease, Huntington disease, among others. Hence, measuring their levels is highly important for early diagnosis, therapy, and disease prognosis. In this work, we investigate facile functionalization methods to tune and enhance sensitivity of printed graphene sensors to neurotransmitters. Sensors based on direct laser scribing and screen-printed graphene ink are studied. These printing methods offer ease of prototyping and scalable fabrication at low cost.
The effect of functionalization of laser induced graphene (LIG) by electrodeposition and solution-based deposition of TMDs (molybdenum disulfide2and tungsten disulfide) and metal nanoparticles is studied. For different processing methods, electrochemical characteristics (such as electrochemically active surface area: ECSA and heterogenous electron transfer rate: k0) are extracted and correlated to surface chemistry and defect density obtained respectively using X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. These functionalization methods are observed to directly impact the sensitivity and limit of detection (LOD) of the graphene sensors for the studied neurotransmitters. For example, as compared to bare LIG, it is observed that electrodeposition of MoS2on LIG improves ECSA by 3 times and k0by 1.5 times.3Electrodeposition of MoS2also significantly reduces LOD of serotonin and dopamine in saliva, enabling detection of their physiologically relevant concentrations (in pM-nM range). In addition, chemical treatment of LIG sensors is carried out in the form of acetic acid treatment. Acetic acid treatment has been shown previously to improve C-C bonds improving the conductivity of LIG sensors.4In our work, in particular, acetic acid treatment leads to larger improvement of LOD of norepinephrine compared to MoS2electrodeposition.
In addition, we investigate the effect of plasma treatment to tune the sensor response by modifying the defect density and chemistry. For example, we find that oxygen plasma treatment of screen-printed graphene ink greatly improves LOD of norepinephrine up to three orders of magnitude, which may be attributed to the increased defects and oxygen functional groups on the surface as evident by XPS measurements. Defects are known to play a key role in enhancing the sensitivity of 2D materials to surface interactions, and have been explored in tuning/enhancing the sensor sensitivity.5Building on our previous work,3we apply a custom machine learning-based data processing method to further improve that sensitivity and LOD, and also to automatically benchmark different molecule-material pairs.
Future work includes expanding the plasma chemistry and conditions, studying the effect of precursor mixture in laser-induced solution-based functionalization, and understanding the interplay between molecule-material system. Work is also underway to improve the machine learning model by using nonlinear learning models such as neural networks to improve the sensor sensitivity, selectivity, and robustness.
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Sci. Adv. 6 , 4250–4257 (2020).V. Kammarchedu, D. Butler, A. Ebrahimi,
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