A highly sensitive electrochemical microRNA-21 biosensor based on intercalating methylene blue signal amplification and a highly dispersed gold nanoparticles/graphene/polypyrrole composite.

Numerous clinical studies suggest that microRNAs (miRNAs) are indicative biomolecules for the early diagnosis of cancer. This work aims to develop a cost-effective and label-free electrochemical biosensor to detect miRNA-21, a biomarker of breast cancer. An electrochemical sensor is fabricated using a nanocomposite, consisting of graphene (GP), polypyrrole (PPY) and gold nanoparticles (AuNPs), modified onto a screen-printed carbon electrode (SPCE) to improve electron transfer properties and increase the degree of methylene blue (MB) intercalation for signal amplification. The GP/PPY-modified electrode offers good electrochemical reactivity and high dispersibility of AuNPs, resulting in excellent sensor performance. Peak current of the MB redox process, which is proportional to miRNA-21 concentration on the electrode surface, is monitored by differential pulse voltammetry (DPV). Under optimal conditions, this sensor is operated by monitoring the MB signal response due to the amount of hybridization products between miRNA-21 target molecules and DNA-21 probes immobilized on the electrode. The proposed biosensor reveals a linear range from 1.0 fM to 1.0 nM with a low detection limit of 0.020 fM. In addition, the miRNA-21 biosensor provides good selectivity, high stability, and satisfactory reproducibility, which shows promising potential in clinical research and diagnostic applications.

Development of electrochemical biosensors for simultaneous multiplex detection of microRNA for breast cancer screening.

A highly sensitive electrochemical biosensors has been developed for the detection of multiplex micro ribonucleic acids (miRNAs) by modifying an electrode with reduced graphene oxide/poly(2-aminobenzylamine)/gold nanoparticles and adopting porous, hollow silver-gold nanoparticles as tagged labeling with metal ions. In addition, an anti-deoxyribonucleic acid (DNA)-RNA hybrid [S9.6] antibody was used to detect different hybridized capture DNAs and miRNAs that can detect multiple miRNAs simultaneously. The developed electrochemical platform exhibits high selectivity, stability, and sensitivity with a wide linear range from 1 fM to 10 nM and a low detection limit of 0.98 fM, 3.58 fM, and 0.25 fM for miRNA-155, miRNA-21, and miRNA-16, respectively. In addition, the proposed electrochemical biosensor capable for the simultaneous detection of miRNA-155, miRNA-16, and miRNA-21, which are breast cancer biomarkers, in normal human serum, can be adopted and potentially used for breast cancer screening.

Highly scalable, uniform, and sensitive biosensors based on top-down indium oxide nanoribbons and electronic enzyme-linked immunosorbent assay.

Nanostructure field-effect transistor (FET) biosensors have shown great promise for ultra sensitive biomolecular detection. Top-down assembly of these sensors increases scalability and device uniformity but faces fabrication challenges in achieving the small dimensions needed for sensitivity. We report top-down fabricated indium oxide (In2O3) nanoribbon FET biosensors using highly scalable radio frequency (RF) sputtering to create uniform channel thicknesses ranging from 50 to 10 nm. We combine this scalable sensing platform with amplification from electronic enzyme-linked immunosorbent assay (ELISA) to achieve high sensitivity to target analytes such as streptavidin and human immunodeficiency virus type 1 (HIV-1) p24 proteins. Our approach circumvents Debye screening in ionic solutions and detects p24 protein at 20 fg/mL (about 250 viruses/mL or about 3 orders of magnitude lower than commercial ELISA) with a 35% conduction change in human serum. The In2O3 nanoribbon biosensors have 100% device yield and use a simple 2 mask photolithography process. The electrical properties of 50 In2O3 nanoribbon FETs showed good uniformity in on-state current, on/off current ratio, mobility, and threshold voltage. In addition, the sensors show excellent pH sensitivity over a broad range (pH 4 to 9) as well as over the physiological-related pH range (pH 6.8 to 8.2). With the demonstrated sensitivity, scalability, and uniformity, the In2O3 nanoribbon sensor platform makes great progress toward clinical testing, such as for early diagnosis of acquired immunodeficiency syndrome (AIDS).

Aligned epitaxial SnO2 nanowires on sapphire: growth and device applications.

Semiconducting SnO2 nanowires have been used to demonstrate high-quality field-effect transistors, optically transparent devices, photodetectors, and gas sensors. However, controllable assembly of rutile SnO2 nanowires is necessary for scalable and practical device applications. Here, we demonstrate aligned, planar SnO2 nanowires grown on A-plane, M-plane, and R-plane sapphire substrates. These parallel nanowires can reach 100 µm in length with sufficient density to be patterned photolithographically for field-effect transistors and sensor devices. As proof-of-concept, we show that transistors made this way can achieve on/off current ratios on the order of 10(6), mobilities around 71.68 cm(2)/V·s, and sufficiently high currents to drive external organic light-emitting diode displays. Furthermore, the aligned SnO2 nanowire devices are shown to be photosensitive to UV light with the capability to distinguish between 254 and 365 nm wavelengths. Their alignment is advantageous for polarized UV light detection; we have measured a polarization ratio of photoconductance (σ) of 0.3. Lastly, we show that the nanowires can detect NO2 at a concentration of 0.2 ppb, making them a scalable, ultrasensitive gas sensing technology. Aligned SnO2 nanowires offer a straightforward method to fabricate scalable SnO2 nanodevices for a variety of future electronic applications.

Highly Sensitive and Quick Detection of Acute Myocardial Infarction Biomarkers Using In2O3 Nanoribbon Biosensors Fabricated Using Shadow Masks.

We demonstrate a scalable and facile lithography-free method for fabricating highly uniform and sensitive In2O3 nanoribbon biosensor arrays. Fabrication with shadow masks as the patterning method instead of conventional lithography provides low-cost, time-efficient, and high-throughput In2O3 nanoribbon biosensors without photoresist contamination. Combined with electronic enzyme-linked immunosorbent assay for signal amplification, the In2O3 nanoribbon biosensor arrays are optimized for early, quick, and quantitative detection of cardiac biomarkers in diagnosis of acute myocardial infarction (AMI). Cardiac troponin I (cTnI), creatine kinase MB (CK-MB), and B-type natriuretic peptide (BNP) are commonly associated with heart attack and heart failure and have been selected as the target biomarkers here. Our approach can detect label-free biomarkers for concentrations down to 1 pg/mL (cTnI), 0.1 ng/mL (CK-MB), and 10 pg/mL (BNP), all of which are much lower than clinically relevant cutoff concentrations. The sample collection to result time is only 45 min, and we have further demonstrated the reusability of the sensors. With the demonstrated sensitivity, quick turnaround time, and reusability, the In2O3 nanoribbon biosensors have shown great potential toward clinical tests for early and quick diagnosis of AMI.

Black phosphorus gas sensors.

The utilization of black phosphorus and its monolayer (phosphorene) and few-layers in field-effect transistors has attracted a lot of attention to this elemental two-dimensional material. Various studies on optimization of black phosphorus field-effect transistors, PN junctions, photodetectors, and other applications have been demonstrated. Although chemical sensing based on black phosphorus devices was theoretically predicted, there is still no experimental verification of such an important study of this material. In this article, we report on chemical sensing of nitrogen dioxide (NO2) using field-effect transistors based on multilayer black phosphorus. Black phosphorus sensors exhibited increased conduction upon NO2 exposure and excellent sensitivity for detection of NO2 down to 5 ppb. Moreover, when the multilayer black phosphorus field-effect transistor was exposed to NO2 concentrations of 5, 10, 20, and 40 ppb, its relative conduction change followed the Langmuir isotherm for molecules adsorbed on a surface. Additionally, on the basis of an exponential conductance change, the rate constants for adsorption and desorption of NO2 on black phosphorus were extracted for different NO2 concentrations, and they were in the range of 130-840 s. These results shed light on important electronic and sensing characteristics of black phosphorus, which can be utilized in future studies and applications.