Solution-gated Graphene Transistors Research Articles

N/S co-doped carbon dots-based solution-gated graphene transistors (SGGT) for ultra-sensitive and selective determination of Hg (II) ions in real water and serum samples

The conventional methods for detecting Hg2+ ions are generally impaired by low sensitivity, a high limit of detection (LOD), and the long detection time required. In this work, we develop a novel solution gated graphene transistor (SGGT) based on carbon dots doped with N and S elements (N/S CDs) as gate electrode probes. The prepared N/S CDs, which are 3–5 nm in diameter, are first modified at the gate of the SGGT through covalent bonding that specifically recognizes Hg2+ ions. The SGGT is then used as a Hg2+ sensor, exhibiting good selectivity, ultrahigh sensitivity, good reproducibility, and a short detection time. The SGGT sensor has an excellent linear detection range, from 0.1 fM to 1 nM. The LOD can reach 28 aM, which is far lower than that of conventional detection methods. Moreover, the SGGT sensor also has a rapid response time of ∼ 40 s. Finally, the ability to analyze real water samples and serum samples is demonstrated.

Ultrahighly Sensitive and Selective Glutathione Sensor Based on Carbon Dot-Functionalized Solution-Gate Graphene Transistor.

A new type of carbon dot (CD)-functionalized solution-gated graphene transistor (SGGT) sensor was designed and fabricated for the highly sensitive and highly selective detection of glutathione (GSH). The CDs were synthesized via a one-step hydrothermal method using DL-thioctic acid and triethylenetetramine (TETA) as sources of S, N, and C. The CDs have abundant amino and carboxyl groups and were used to modify the surface of the gate electrode of SGGT as probes for detecting GSH. Remarkably, the CDs-SGGT sensor exhibited excellent selectivity and ultrahigh sensitivity to GSH, with an ultralow limit of detection (LOD) of up to 10-19 M. To the best of our knowledge, the sensor outperforms previously reported systems. Moreover, the CDs-SGGT sensor shows rapid detection and good stability. More importantly, the detection of GSH in artificial serum samples was successfully demonstrated.

Selective detection of Pb2+ ions based on a graphene field-effect transistor gated by DNAzymes in binding mode

Heavy metal contamination has become a severe threat to dairy products through contaminated feed and the environment water. Among them, Pb(II) is highly toxic to the human body even under minimal exposure. Therefore, establishing a fast and sensitive Pb2+ detection technology is significant for rapid screening of vast number of dairy products. Hererin, we report the development of a sensitive and selective Pb(II) biosensor based on a solution-gated graphene transistor (SGGT) with the gate modified by Pb2+-dependent DNAzyme probes. It has also been explored that the DNAzymes working in simple binding mode integrate better with the SGGT than those working in normal catalytic mode, showing significantly stronger channel current responses and lower detection limit down to 0.39 μg/L (or 1.9 nM). Finally, the biosensor was practicably applied to the detection of lead ions in pure milk samples with a high recovery rate. We believe that this work reveals the best strategy for integrating metal ion dependent DNAzyme probes with SGGT sensing platforms to selectively and sensitively detect many metal ions.

Unamplified and Label-Free Detection of HPV16 DNA Using CRISPR-Cas12a-Functionalized Solution-Gated Graphene Transistors.

The persistent infection of high-risk-human papillomavirus type 16 (HPV16) is considered an essential element for suffering cervical cancer. Despite polymerase chain reaction, loop-mediated amplification, and microfluidicchips are used to detect the HPV16, these methods still exist some drawbacks including time-consuming and false positive results. The CRISPR-Cas system is widely used in the region of biological detection due to its precise targeted recognition capability. In this contribution, the novel solution-gated graphene transistor sensor is designed to realize the unamplified and label-free detection of HPV16 DNA. Using the precise recognition of the CRISPR-Cas12a system and the gate functionalization, HPV16 DNA can be precisely identified without need the amplification and labeling. The limit of detection of the sensor can be up to 8.3×10-18 m and the detection can be within 20min. Additionally, the heat-Inactivated clinical samples can be clearly distinguished by the sensor the diagnosis results have a high degree of agreement with q-PCR detection.

Highly sensitive and real-time detection of sialic acid using a solution-gated graphene transistor functionalized with carbon quantum dots

Sialic acid (SA) involves multiple different physiological and pathological processes. The SA level in serum is a reliable biomarker for the early diagnosis of malignant tumors. In this study, a new type of solution-gated graphene transistor was designed and fabricated for highly sensitive and real-time detection of SA by rapid binding of boric acid groups to diol monosaccharides. The gate electrode was modified with synthesized carbon quantum dots having boronic acid on the surface as the specific recognition site of SA. The detection of SA is achieved via the change of the gate surface potential after the conjugation of SA with carbon quantum dots. The device sensitivity can reach 10−19 M and a good linear relationship was present between the electrical current response and logarithmic values of the SA concentrations in the range of 10−19 M to 10−5 M. This sensor also exhibited good selectivity and good stability. Furthermore, the detection of SA in simulated serum samples was also carried out and satisfactory results were acquired, showing the high potential of the prepared sensor in clinical application.

Carbon Dot-Functionalized Solution-Gated Graphene Transistors for Highly Sensitive Detection of Cobalt(II) Ions

A carbon dot-functionalized solution-gated graphene transistor (CD-SGGT) was designed and prepared via the modification of CDs on the gate of SGGT. The above CDs were hydrothermally synthesized using DL-thioctic acid and triethylenetramine as C, N and S sources. The average size of CDs was ~6.2 nm, and there were many amino and carboxyl groups on the CDs’ surfaces. The CDs was then used as a probe for preparation of CD-SGGT sensor for the cobalt(II) (Co2+) ions detection. The CD-SGGT sensor showed excellent sensitivity and high selectivity. Remarkably, the limit of detection (LOD) reached 10−19 M. The linear detection range was obtained from 10−19 to 10−15 M. Additionally, the CD-SGGT also showed fast response and good stability.

Graphene electrochemical transistor incorporated with gel electrolyte for wearable and non-invasive glucose monitoring

With the rapid development of wearable electronic devices, health monitoring is undergoing a fundamental shift from hospital-centered treatment to patient-centered diagnosis. Solution-gated graphene transistors provide an effective platform for developing high-sensitivity wearable devices due to their unique signal amplification, low energy consumption, and compatibility for miniaturization. However, it is still a major challenge to perform real-time sweat composition monitoring directly on the dry skin surface. In this work, a skin-based flexible gel electrolyte graphene transistor (GEGT) was successfully designed and fabricated for glucose detection, consisting of a gate electrode decorated with Au nanoparticles modified reduced graphene oxide (AuNPs/RGO) nanocomposites and a monolayer graphene channel. Glycerin gel was used to replace the traditional liquid electrolyte, not only could better fit the human skin, but also play the role of fluid collection, providing stable testing conditions for the sensor. Based on the high electron mobility of graphene channel and the excellent electrocatalytic performance of AuNPs/RGO nanocomposites, the constructed GEGT sensor exhibits excellent sensing performance for glucose with good selectivity, low operating voltage (0.5 V), wide detection range (10 nM - 25 mM), and low detection limit (10 nM). The device maintains stable performance after up to 1000 bending cycles with a bending radius of 4 mm. In addition, the GEGT sensor displays good accuracy in sweat detection and sensitive dynamic response during actual wearing, which provides a guarantee for the construction of wearable transistor devices and real-time health tracking.

Unamplified and Real-Time Label-Free miRNA-21 Detection Using Solution-Gated Graphene Transistors in Prostate Cancer Diagnosis.

The incidence of prostate cancer (PCa) in men globally increases as the standard of living improves. Blood serum biomarker prostate-specific antigen (PSA) detection is the gold standard assay that do not meet the requirements of early detection. Herein, a solution-gated graphene transistor (SGGT) biosensor for the ultrasensitive and rapid quantification detection of the early prostate cancer-relevant biomarker, miRNA-21 is reported. The designed single-stranded DNA (ssDNA) probes immobilized on the Au gate can hybridize effectively with the miRNA-21 molecules targets and induce the Dirac voltage shifts of SGGT transfer curves. The limit of detection (LOD) of the sensor can reach 10-20 M without amplification and any chemical or biological labeling. The detection linear range is from 10-20 to 10-12 M. The sensor can realize real-time detection of the miRNA-21 molecules in less than 5 min and can well distinguish one-mismatched miRNA-21 molecule. The blood serum samples from the patients without RNA extraction and amplification are measured. The results demonstrated that the biosensor can well distinguish the cancer patients from the control group and has higher sensitivity (100%) than PSA detection (58.3%). Contrastingly, it can be found that the PSA level is not directly related to PCa.

Rapid and Unamplified Detection of SARS-CoV-2 RNA via CRISPR-Cas13a-Modified Solution-Gated Graphene Transistors.

The disease caused by severe acute respiratory syndrome coronavirus, SARS-CoV-2, is termed COVID-19. Even though COVID-19 has been out for more than two years, it is still causing a global pandemic. Due to the limitations of sample collection, transportation, and kit performance, the traditional reverse transcription-quantitative polymerase chain reaction (RT-qPCR) method has a long detection period and high testing costs. An increased risk of infection is inevitable, since many patients may not be diagnosed in time. The CRISPR-Cas13a system can be designed for RNA identification and knockdown, as a promising platform for nucleic acid detection. Here, we designed a solution-gated graphene transistor (SGGT) biosensor based on the CRISPR-Cas13a system. Using the gene-targeting capacity of CRISPR-Cas13a and gate functionalization via multilayer modification, SARS-CoV-2 nucleic acid sequences can be quickly and precisely identified without the need for amplification or fluorescence tagging. The limit of detection (LOD) in both buffer and serum reached the aM level, and the reaction time was about 10 min. The results of the detection of COVID-19 clinical samples from throat swabs agree with RT-PCR. In addition, the interchangeable gates significantly minimize the cost and time of device fabrication. In a nutshell, our biosensor technology is broadly applicable and will be suitable for point-of-care (POC) testing.

Determination of sunset yellow in beverage based on solution-gated graphene transistors with multi-walled carbon nanotube functionalized gate electrodes

• A sunset yellow sensor based on solution-gated graphene transistor is proposed. • The sensor is modified by multi-walled carbon nanotubes and chitosan. • The sensor has a detection limit as low as 300 nM. • The sensor can be used for sunset yellow content in actual samples. Sunset yellow, one of the most widely used synthetic pigments in the food industry, may cause an adverse reaction in the human body due to its cytotoxicity and potential genotoxicity when overdosed. Developing a rapid, low-cost, and convenient detection method for the sunset yellow pigment is necessary. In this study, we report the fabrication of a highly sensitive and selective sensor for sunset yellow detection based on solution-gated graphene transistors (SGGT). To improve the performance of the SGGT-based sensor, we modified the Au gate electrode with multi-walled carbon nanotubes (MWCNTs). The detection limit of the MWCNT-modified SGGT sensor was 100 nM, and the linear range was from 300 nM to 100 μM. More importantly, the SGGTs sensor showed a selective response to sunset yellow. Finally, we demonstrated that the optimized SGGT-based sensor could detect the concentration of sunset yellow in Fanda soft drink. Therefore, we believe that the SGGT-based sensor with the reported effective modification can be used in the field of food safety and quality control, providing a promising platform for detecting many other analytes.

Breath alcohol sensor based on hydrogel-gated graphene field-effect transistor

The inspection of drunk driving has become an effective measure to reduce the occurrence of traffic accidents. In this work, we constructed a breath alcohol biosensor based on a hydrogel-gated graphene field-effect transistor (HGGT) with chlorella derived layered carbon nanosheets (CNs) and alcohol oxidase (AOx) embedded in the hydrogel. The sensing mechanism of the AOx/CNs functionalized sensor lies in the oxidation reaction of alcohol by AOx and the electrocatalytic oxidation reaction of the generated H2O2. The HGGT based alcohol sensor exhibited an excellent sensitivity with a very low detection limit down to 1 μM (i.e. 0.046 ppm), and has been successfully applied to breath alcohol test after drinking. Compared with normal solution-gated graphene transistors, employment of hydrogel as a source of electrolytes greatly enhances the portability of the sensor, and facilitates functionalization with enzymes and nanomaterials. Due to the advantages of real-time, high portability and accuracy of the functionalized HGGT sensor, it demonstrates a promising platform for constructing biosensors for many other analytes.

Ultrasensitive Label-Free DNA Detection Based on Solution-Gated Graphene Transistors Functionalized with Carbon Quantum Dots.

Developing highly sensitive, reliable, cost-effective label-free DNA biosensors is challenging with traditional fluorescence, electrochemical, and other techniques. Most conventional methods require labeling fluorescence, enzymes, or other complex modification. Herein, we fabricate carbon quantum dot (CQD)-functionalized solution-gated graphene transistors for highly sensitive label-free DNA detection. The CQDs are immobilized on the surface of the gate electrode through mercaptoacetic acid with the thiol group. A single-stranded DNA (ssDNA) probe is immobilized on CQDs by strong π-π interactions. The ssDNA probe can hybridize with the ssDNA target and form double-stranded DNA, which led to a shift of Dirac voltage and the channel current response. The limit of detection can reach 1 aM which is 2-5 orders of magnitude lower than those of other methods reported previously. The sensor also exhibits a good linear range from 1 aM to 0.1 nM and has good specificity. It can effectively distinguish one-base mismatched target DNA. The response time is about 326 s for the 1 aM target DNA molecules. This work provides good perspectives on the applications in biosensors.

Determination of Sunset Yellow in Beverage Based on Solution-Gated Graphene Transistors with Multi-Walled Carbon Nanotube Functionalized Gate Electrodes

Determination of Sunset Yellow in Beverage Based on Solution-Gated Graphene Transistors with Multi-Walled Carbon Nanotube Functionalized Gate Electrodes

Highly Sensitive Detection of Cobalt(Ii) Ions Based on Carbon Dot-Functionalized Solution-Gated Graphene Transistors

Highly Sensitive Detection of Cobalt(Ii) Ions Based on Carbon Dot-Functionalized Solution-Gated Graphene Transistors

The Gate-Modified Solution-Gated Graphene Transistors for the Highly Sensitive Detection of Lead Ions.

Lead ions are heavy metal ions that are extremely harmful to the human body and ecological environment. They can cause irreversible damage to the human nervous system and blood system at low concentrations. It is very important to develop a simple, rapid, and sensitive detection method of Pb2+. Solution-gated graphene transistors (SGGTs) have been widely studied in recent years due to their ultra-high sensitivity in chemical sensing. Herein, we have demonstrated a sensitive sensor of Pb2+ based on the SGGTs through the glutathione gate modification. When Pb2+ are added into the electrolyte solution, the electrical double layer capacitance near the gate electrode changes because Pb2+ can be strongly chelated, leading to the channel current change. The detection of Pb2+ can be realized. The detection limit of sensors for Pb2+ can reach 1 × 10-18 M, and the response time is about 1 s. The channel current change and the logarithm of Pb2+ concentration exhibit a good linear relationship in the concentration range of 1 × 10-18 and 1 × 10-6 M. Because the glutathione molecule can well recognize Pb2+, the devices also demonstrate good selectivity to Pb2+. Compared with the convention detection, our method shows easy operation, high sensitivity, and high selectivity. Therefore, it has great potential in the analysis of trace samples for health and environment monitoring.

Aptamer-Based Solution-Gated Graphene Transistors for Highly Sensitive and Real-Time Detection of Thrombin Molecules.

Thrombin is an important biomarker for various diseases and biochemical reactions. Rapid and real-time detection of thrombin that quickly neutralizes in early coagulation in the body has gained significant attention for its practical applications. Solution-gated graphene transistors (SGGTs) have been widely studied due to their higher sensitivity and low-cost fabrication for chemical and biological sensing applications. In this paper, the ssDNA aptamer with 29 bases was immobilized on the surface of the gate electrode to specifically recognize thrombin. The SGGT sensor achieved high sensitivity with a limit of detection (LOD) up to fM. The LOD was attributed to the amplification function of SGGTs and the suitable aptamer choice. The ssDNA configuration folding induced by thrombin molecules and the electropositivity of thrombin molecules could arouse the same electrical response of SGGTs, helping the device obtain a high sensitivity. The channel current variation of sensors had a good linear relationship with the logarithm of thrombin concentration in the range of 1 fM to 10 nM. The fabricated device also demonstrated a short response time to thrombin molecules, and the response time to the 1 fM thrombin molecules was about 150 s. In summary, the sensing strategy of aptamer-based SGGTs with high sensitivity and high selectivity has a good prospect in medical diagnosis.

An Acetylcholinesterase-Functionalized Biosensor for Sensitive Detection of Organophosphorus Pesticides Based on Solution-Gated Graphene Transistors

In this work, a highly sensitive and selective organophosphorus pesticide (OP) biosensor based on a solution-gated graphene transistor (SGGT) has been successfully constructed. The electrochemical performance of the device is improved by immobilization of acetylcholinesterase (AChE) on the gold gate electrode with chitosan (CHIT) for detection of OPs. The AChE/CHIT-functionalized SGGT sensor shows an ultralow detection limit of 10 nM for OPs and a wide linear range from 300 nM to 3 μM. We also proved that the SGGT-based OP sensor has good selectivity and recovery performance for efficient evaluation of the level of OPs in actual rice samples. This sensor provides a promising detection platform for rapid and sensitive analysis of OPs in real samples with complex components and can be readily applied to many other important analytes for agricultural and food safety using the corresponding enzymes.

Solution-gated graphene transistor based sensor for histamine detection with gold nanoparticles decorated graphene and multi-walled carbon nanotube functionalized gate electrodes

In order to achieve accurate detection and evaluation of the freshness of fish samples, high sensitivity and selectivity of histamine sensors based on solution-gated graphene transistors (SGGT) have been successfully developed. By using graphene (Gra), multi-walled carbon nanotubes (MWNT) and gold nanoparticles (AuNP) to functionalize the gate electrode, the electrocatalytic performance of the device can be significantly improved. We have found that graphene, MWNT and AuNP modified SGGT sensors exhibit an ultra-low detection limit of 100 nM for histamine, a linear range of 3 μM–100 μM. We have also demonstrated that the SGGT-based histamine sensor has a high recovery rate and is capable of assessing the histamine content of actual fish samples in a fast and accurate manner. Considering the superior performance of the SGGT-based histamine sensor, it can be readily extended to histamine determination in many other real food samples for their freshness assessment.

Construction of highly accessible single Co site catalyst for glucose detection

The development of high-performance glucose sensors is an urgent need, especially for diabetes mellitus diagnosis. However, the glucose monitoring is conventionally operated in an invasive finger-prick manner and their noninvasive alternatives largely suffered from the relatively poor sensitivity, selectivity, and stability, resulted from the lack of robust and efficient catalysts. In this paper, we design a concave shaped nitrogen-doped carbon framework embellished with single Co site catalyst (Co SSC) by selectively controlling the etching rate on different facet of carbon substrate, which is beneficial to the diffusion and contact of analyte. The Co SSC prompts a significant improvement in the sensitivity of the solution-gated graphene transistor (SGGT) devices, with three orders of magnitude better than those of SGGT devices without catalysts. Our findings expand the field of single site catalyst in the application of biosensors, diabetes diagnostics and personalized health-care monitoring.

Single-Atom Enzyme-Functionalized Solution-Gated Graphene Transistor for Real-Time Detection of Mercury Ion.

Mercury ion (Hg2+), a bioaccumulating and toxic heavy metal, can cause severe damages to the environment and human health. Therefore, development of high-performance Hg2+ sensors is highly desirable. Herein, we construct a uniform dodecahedral shaped N-doped carbon decorated by single Fe site enzyme (Fe-N-C SAE), which exhibits good performance for Hg2+ detection. The N atom on Fe-N-C SAE can specifically recognize Hg2+ through chelation between Hg2+ and N atom, while the catalytic site on the single-atom enzyme acts as a signal amplifier. The Fe-N-C SAE-functionalized solution-gated graphene transistor exhibits a dramatic improvement in the selectivity and sensitivity of the devices. The sensor can rapidly detect Hg2+ down to 1 nM within 2 s. Besides, a relatively good repeatability and reproducibility for the detection of Hg2+ have also been found in our sensor platform. Our findings expand the application of single-atom catalysts in the field of food safety and environmental monitoring.