MXenes - Versatile 2D materials for identification of biomarkers and contaminants in large scale environments - A review

Recent years have seen a lot of interest in transition metal carbides/carbonitrides (MXenes), Which is one of newly proliferating two-dimensional (2D) materials.The advantages and applications of synthesizing MXenes-based biosensing systems are interesting. There is an urgent requirement for synthesis of MXenes. Through foliation, physical adsorption, and interface modification,it has been proposed that many biological disorders are related to genetic mutation. Majority of mutations were discovered to be nucleotide mismatches. Consequently, accurate -nucleotide mismatched discrimination is crucial for both diagnosing and treating diseases. To differentiate between such a sensitivealterations in the DNA duplex, several detection methods, particularly Electrochemical-luminescence (ECL) ones, have really been investigated.M_n+1X_nT_x is common name for MXenes, a novel family of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, where T stands for interface termination units (i.e. = O, OH, and/or F). These electronic characteristics of MXenes may be changed between conductive to semiconducting due to abundant organometallic chemistry.Solid-state ECL sensors predicated on MXene would provide the facile nucleotide detection and convenience for usage with minimal training, mobility and possibly minimal cost.This study emphasizes upcoming requirements and possibilities in this area while describing the accomplishments achieved in the usage and employing of MXenes in the research and development of facile biomarkerdetection and their significance in designing electrochemical sensors. Opportunities are addressed for creating 2D MXene materials sensors and devices with incorporated biomolecule sensing. MXenes Carry out this process sensors, address the advantages of using MXenes and their variants as detecting materials for gathering different types of data, and attempt to clarify the design principles and operation of related MXene-based sensors, such as nucleotide detection, Single nucleotide detectors, Cancer theranostics, Biosensing capabilities, Gliotoxin detection, SARS-COV-2 nucleocapsid detection, electrochemical sensors, visual sensors, and humidity sensors. Finally, we examine the major issues and prospects for MXene-based materials used in various sensing applications.

DNA sequencing by Förster resonant energy transfer

We propose a new DNA sequencing concept based on nonradiative Förster resonant energy transfer (FRET) from a donor quantum dot (QD) to an acceptor molecule. The FRET mechanism combined with the nanopore-based DNA translocation is suggested as a novel concept for sequencing DNA molecules. A recently-developed hybrid quantum/classical method is employed, which uses time-dependent density functional theory and quasistatic finite difference time domain calculations. Due to the significant absorbance of DNA bases for photon energies higher than 4 eV, biocompatibility, and stability, we use Zinc-Oxide (ZnO) QD as a donor in the FRET mechanism. The most sensitivity for the proposed method to DNA is achieved for the Hoechst fluorescent-dye acceptor and 1 nm ZnO-QD. Results show that the insertion of each type of DNA nucleobases between the donor and acceptor changes the frequency of the emitted light from the acceptor molecule between 0.25 to 1.6 eV. The noise analysis shows that the method can determine any unknown DNA nucleobases if the signal-to-noise ratio is larger than 5 dB. The proposed concept and excellent results shed light on a new promising class of DNA sequencers.

Interband plasmon-enhanced optical absorption of DNA nucleobases through the graphene nanopore

We propose a novel, to the best of our knowledge, plasmonic-based methodology for the purpose of fast DNA sequencing. The interband surface plasmon resonance and field-enhancement properties of graphene nanopore in the presence of the DNA nucleobases are investigated using a hybrid quantum/classical method (HQCM), which employs time-dependent density functional theory and a quasistatic finite difference time domain approach. In the strong plasmonic-molecular coupling regime where the plasmon and DNA absorption frequencies are degenerated, the optical response of DNA molecule in the vicinity of the nanopore is enhanced. In contrast, when the plasmon and nucleobases resonances are detuned the distinct peaks and broadening of the molecular resonances represent the inherent properties of the nucleobase. Due to the different optical properties of DNA nucleobases in the ultraviolet (UV) region of light, the signal corresponding to the replacement of nucleobases in a DNA block can be determined by considering the differential absorbance. Results show the promising capability of the present mechanism for practical DNA sequencing.

Ultrasensitive Detection of Dopamine, IL-6 and SARS-CoV-2 Proteins on Crumpled Graphene FET Biosensor

Universal platforms for biomolecular analysis using label-free sensing modalities can address important diagnostic challenges. Electrical field effect-sensors are an important class of devices that can enable point-of-care sensing by probing the charge in the biological entities. Use of crumpled graphene for this application is especially promising. It is previously reported that the limit of detection (LoD) on electrical field effect-based sensors using DNA molecules on the crumpled graphene FET (field-effect transistor) platform. Here, the crumpled graphene FET-based biosensing of important biomarkers including small molecules and proteins is reported. The performance of devices is systematically evaluated and optimized by studying the effect of the crumpling ratio on electrical double layer (EDL) formation and bandgap opening on the graphene. It is also shown that a small and electroneutral molecule dopamine can be captured by an aptamer and its conformation change induced electrical signal changes. Three kinds of proteins were captured with specific antibodies including interleukin-6 (IL-6) and two viral proteins. All tested biomarkers are detectable with the highest sensitivity reported on the electrical platform. Significantly, two COVID-19 related proteins, nucleocapsid (N-) and spike (S-) proteins antigens are successfully detected with extremely low LoDs. This electrical antigen tests can contribute to the challenge of rapid, point-of-care diagnostics.

Highly sensitive crumpled 2D material-based plasmonic biosensors

We propose surface plasmon resonance biosensors based on crumpled graphene and molybdenum disulphide (MoS₂) flakes supported on stretchable polydimethylsiloxane (PDMS) or silicon substrates. Accumulation of specific biomarkers resulting in measurable shifts in the resonance wavelength of the plasmon modes of two-dimensional (2D) material structures, with crumpled structures demonstrating large refractive index shifts. Using theoretical calculations based on the semiclassical Drude model, combined with the finite element method, we demonstrate that the interaction between the surface plasmons of crumpled graphene/MoS₂ layers and the surrounding analyte results in high sensitivity to biomarker driven refractive index shifts, up to 7499 nm/RIU for structures supported on silicon substrates. We can achieve a high figure of merit (FOM), defined as the ratio of the refractive index sensitivity to the full width at half maximum of the resonant peak, of approximately 62.5 RIU^-1. Furthermore, the sensing properties of the device can be tuned by varying crumple period and aspect ratio through simple stretching and integrating material interlayers. By stacking multiple 2D materials in heterostructures supported on the PDMS layer, we produced hybrid plasmon resonances detuned from the PDMS absorbance region allowing higher sensitivity and FOM compared to pure crumpled graphene structures on the PDMS substrates. The high sensitivity and broad mechanical tunability of these crumpled 2D material biosensors considerable advantages over traditional refractive index sensors, providing a new platform for ultrasensitive biosensing.

Three-dimensional microscale hanging drop arrays with geometric control for drug screening and live tissue imaging

Existing three-dimensional (3D) culture techniques are limited by trade-offs between throughput, capacity for high-resolution imaging in living state, and geometric control. Here, we introduce a modular microscale hanging drop culture where simple design elements allow high replicates for drug screening, direct on-chip real-time or high-resolution confocal microscopy, and geometric control in 3D. Thousands of spheroids can be formed on our microchip in a single step and without any selective pressure from specific matrices. Microchip cultures from human LN229 glioblastoma and patient-derived mouse xenograft cells retained genomic alterations of originating tumors based on mate pair sequencing. We measured response to drugs over time with real-time microscopy on-chip. Last, by engineering droplets to form predetermined geometric shapes, we were able to manipulate the geometry of cultured cell masses. These outcomes can enable broad applications in advancing personalized medicine for cancer and drug discovery, tissue engineering, and stem cell research.

Ultrasensitive detection of nucleic acids using deformed graphene channel field effect biosensors

Field-effect transistor (FET)-based biosensors allow label-free detection of biomolecules by measuring their intrinsic charges. The detection limit of these sensors is determined by the Debye screening of the charges from counter ions in solutions. Here, we use FETs with a deformed monolayer graphene channel for the detection of nucleic acids. These devices with even millimeter scale channels show an ultra-high sensitivity detection in buffer and human serum sample down to 600 zM and 20 aM, respectively, which are ∼18 and ∼600 nucleic acid molecules. Computational simulations reveal that the nanoscale deformations can form 'electrical hot spots' in the sensing channel which reduce the charge screening at the concave regions. Moreover, the deformed graphene could exhibit a band-gap, allowing an exponential change in the source-drain current from small numbers of charges. Collectively, these phenomena allow for ultrasensitive electronic biomolecular detection in millimeter scale structures.

Ultrasensitive detection of nucleic acids using deformed graphene channel field effect biosensors

Field-effect transistor (FET)-based biosensors allow label-free detection of biomolecules by measuring their intrinsic charges. The detection limit of these sensors is determined by the Debye screening of the charges from counter ions in solutions. Here, we use FETs with a deformed monolayer graphene channel for the detection of nucleic acids. These devices with even millimeter scale channels show an ultra-high sensitivity detection in buffer and human serum sample down to 600 zM and 20 aM, respectively, which are ∼18 and ∼600 nucleic acid molecules. Computational simulations reveal that the nanoscale deformations can form 'electrical hot spots' in the sensing channel which reduce the charge screening at the concave regions. Moreover, the deformed graphene could exhibit a band-gap, allowing an exponential change in the source-drain current from small numbers of charges. Collectively, these phenomena allow for ultrasensitive electronic biomolecular detection in millimeter scale structures.

A potential sensing mechanism for DNA nucleobases by optical properties of GO and MoS2 Nanopores

We propose a new DNA sensing mechanism based on optical properties of graphene oxide (GO) and molybdenum disulphide (MoS2) nanopores. In this method, GO and MoS2 is utilized as quantum dot (QD) nanopore and DNA molecule translocate through the nanopore. A recently-developed hybrid quantum/classical method (HQCM) is employed which uses time-dependent density functional theory and quasi-static finite difference time domain approach. Due to good biocompatibility, stability and excitation wavelength dependent emission behavior of GO and MoS2 we use them as nanopore materials. The absorption and emission peaks wavelengths of GO and MoS2 nanopores are investigated in the presence of DNA nucleobases. The maximum sensitivity of the proposed method to DNA is achieved for the 2-nm GO nanopore. Results show that insertion of DNA nucleobases in the nanopore shifts the wavelength of the emitted light from GO or MoS2 nanopore up to 130 nm. The maximum value of the relative shift between two different nucleobases is achieved by the shift between cytosine (C) and thymine (T) nucleobases, ~111 nm for 2-nm GO nanopore. Results show that the proposed mechanism has a superior capability to be used in future DNA sequencers.

Nano-plasmonic-based structures for DNA sequencing

We propose novel nano-plasmonic-based structures for rapid sequencing of DNA molecules. The optical properties of DNA nucleotides have notable differences in the ultraviolet (UV) region of light. Using nanopore, bowtie, and bowtie-nanopore compound structures, probable application of the surface plasmon resonance (SPR) in DNA sequencing is investigated by employing the discrete dipole approximation method. The effects of different materials like chromium (Cr), aluminum (Al), rhodium (Rh), and graphene (Gr) are studied. We show that for Cr/Al/Gr/Rh, the nucleotide presented shifts the SPR spectra for the nanopore 1/29/5/34 to 14/39/15/67 nm, bowtie 8/2/49/38 to 31/20/79/55 nm, and bowtie-nanopore compound 25/77/5/16 to 80/80/22/39 nm. The Cr-based compound structure shows excellent sensitivity and selectivity which can make it a promising methodology for DNA sequencing.

Heteronanojunctions with atomic size control using a lab-on-chip electrochemical approach with integrated microfluidics

A versatile tool for electrochemical fabrication of heteronanojunctions with nanocontacts made of a few atoms and nanogaps of molecular spacing is presented. By integrating microfluidic circuitry in a lab-on-chip approach, we keep control of the electrochemical environment in the vicinity of the nanojunction and add new versatility for exchanging and controlling the junction's medium. Nanocontacts made of various materials by successive local controlled depositions are demonstrated, with electrical properties revealing sizes reaching a few atoms only. Investigations on benchmark molecular electronics material, trapped between electrodes, reveal the possibility to create nanogaps of size matching those of molecules. We illustrate the interest of a microfluidic approach by showing that exposure of a fabricated molecular junction to controlled high solvent flows can be used as a reliability criterion for the presence of molecular entities in a gap.

Nanotrench for nano and microparticle electrical interconnects

We present a simple and versatile patterning procedure for the reliable and reproducible fabrication of high aspect ratio (10(4)) electrical interconnects that have separation distances down to 20 nm and lengths of several hundreds of microns. The process uses standard optical lithography techniques and allows parallel processing of many junctions, making it easily scalable and industrially relevant. We demonstrate the suitability of these nanotrenches as electrical interconnects for addressing micro and nanoparticles by realizing several circuits with integrated species. Furthermore, low impedance metal-metal low contacts are shown to be obtained when trapping a single metal-coated microsphere in the gap, emphasizing the intrinsic good electrical conductivity of the interconnects, even though a wet process is used. Highly resistive magnetite-based nanoparticles networks also demonstrate the advantage of the high aspect ratio of the nanotrenches for providing access to electrical properties of highly resistive materials, with leakage current levels below 1 pA.