Graphene and its Derivatives-Based Optical Sensors.

Being the first successfully prepared two-dimensional material, graphene has attracted extensive attention from researchers due to its excellent properties and extremely wide range of applications. In particular, graphene and its derivatives have displayed several ideal properties, including broadband light absorption, ability to quench fluorescence, excellent biocompatibility, and strong polarization-dependent effects, thus emerging as one of the most popular platforms for optical sensors. Graphene and its derivatives-based optical sensors have numerous advantages, such as high sensitivity, low-cost, fast response time, and small dimensions. In this review, recent developments in graphene and its derivatives-based optical sensors are summarized, covering aspects related to fluorescence, graphene-based substrates for surface-enhanced Raman scattering (SERS), optical fiber biological sensors, and other kinds of graphene-based optical sensors. Various sensing applications, such as single-cell detection, cancer diagnosis, protein, and DNA sensing, are introduced and discussed systematically. Finally, a summary and roadmap of current and future trends are presented in order to provide a prospect for the development of graphene and its derivatives-based optical sensors.

A gate-tunable symmetric bipolar junction transistor fabricated via femtosecond laser processing.

Two-dimensional (2D) bipolar junction transistors (BJTs) with van der Waals heterostructures play an important role in the development of future nanoelectronics. Herein, a convenient method is introduced for fabricating a symmetric bipolar junction transistor (SBJT), constructed from black phosphorus and MoS2, with femtosecond laser processing. This SBJT exhibits good bidirectional current amplification owing to its symmetric structure. We placed a top gate on one side of the SBJT to change the difference in the major carrier concentration between the emitter and collector in order to further investigate the effects of electrostatic doping on the device performance. The SBJT can also act as a gate-tunable phototransistor with good photodetectivity and photocurrent gain of ß = ∼21. Scanning photocurrent images were used to determine the mechanism governing photocurrent amplification in the phototransistor. These results promote the development of the applications of multifunctional nanoelectronics based on 2D materials.

Carrier Engineering in Polarization-Sensitive Black Phosphorus van der Waals Junctions.

van der Waals p-n heterostructures based on p-type black phosphorus (BP) integrated with other two-dimensional (2D) layered materials have shown potential applications in electronic and optoelectronic devices, including logic rectifiers and polarization-sensitive photodetectors. However, the engineering of carriers transport anisotropy, which is related to the linear dichroism, have not yet been investigated. Here, we demonstrate a novel van der Waals device of orientation-perpendicular BP homojunction based on the anisotropic band structures between the armchair and zigzag directions. The structure exhibits good gate-tunable diode-like rectification characteristics caused by the barrier between the two perpendicular crystal orientations. Moreover, we demonstrate that the unique mechanisms of the polarization-sensitivity properties of this junction are involved with the linear dichroism and the anisotropic carriers transport engineering. These results were verified by the scanning photocurrent images experiments. This work paves the way for 2D anisotropic layered materials for next-generation electronic and optoelectronic devices.

Modulation of photothermal anisotropy using black phosphorus/rhenium diselenide heterostructures.

Manipulating the polarization of an incident beam using two-dimensional materials has become an important research direction towards the development of nano-optical devices. Black phosphorus (BP) and rhenium diselenide (ReSe2) possess excellent in-plane optical anisotropy with optical birefringence in the visible region, which has led to novel applications in polarizing optics and optoelectronics. Herein, the polarization-dependent absorption of BP and ReSe2 and a modulated pump beam is utilized to obtain the photothermal signal from them. The photothermal anisotropy of BP and ReSe2 has been explored using photothermal detection. Then we have defined the photothermal contrast using the ratio of the maximum to the minimum of the photothermal signal. The photothermal contrast of BP and ReSe2 can be obtained accurately by the relationship between the polarization angle of the pump light and the photothermal signal. We demonstrate that a layered BP with different thicknesses can remarkably change the photothermal contrast. In contrast, the photothermal contrast of ReSe2 does not change with the different thicknesses of the samples. Further, the photothermal anisotropies of BP/ReSe2 heterostructures were also explored. The photothermal contrasts of samples were observed to change with different stacking angles indicating that the photothermal anisotropy of heterostructures is dependent on the stacking angle. Our findings provide new prospects for designing novel optical devices based on two-dimensional anisotropic materials, with potential applications in electronics, photonics, and optoelectronics.

Black-Phosphorus-Based Orientation-Induced Diodes.

Despite many decades of research of diodes, which are fundamental components of electronic and photoelectronic devices with p-n or Schottky junctions using bulk or 2D materials, stereotyped architectures and complex technological processing (doping and multiple material operations) have limited future development. Here, a novel rectification device, an orientation-induced diode, assembled using only few-layered black phosphorus (BP) is investigated. The key to its realization is to utilize the remarkable anisotropy of BP in low dimensions and change the charge-transport conditions abruptly along the different crystal orientations. Rectification ratios of 6.8, 22, and 115 can be achieved in cruciform BP, cross-stacked BP junctions, and BP junctions stacked with vertical orientations, respectively. The underlying physical processes and mechanisms can be explained using "orientation barrier" band theory. The theoretical results are experimentally confirmed using localized scanning photocurrent imaging. These orientation-induced optoelectronic devices open possibilities for 2D anisotropic materials with a new degree of freedom to improve modulation in diodes.

Antitumor effects of chi-shen extract from Salvia miltiorrhiza and Paeoniae radix on human hepatocellular carcinoma cells.

AIM: To investigate the antihepatocellular carcinoma effects of chi-shen extract (CSE) from the water-soluble compounds of Salvia miltiorrhiza and Paeoniae radix. METHODS: The effect of CSE on the growth of HepG2 cells (hepatocellular carcinoma cell line) was studied by 3-(4,5)-2,5-diphenyltetrazolium bromide assay. Apoptosis were detected through acridine orange (AO) and ethylene dibromide (EB) staining and DNA fragmentation assay. The effect of CSE on the cell cycle of HepG2 cells was studied by the propidium iodide staining method. The activation of caspases-3, -8 and -9 was examined by immunoassay kits. The transcription of the Bcl-2 family and p53 was detected by RT-PCR. RESULTS: Our data revealed that CSE strongly induced HepG2 cell death in a dose- and time-dependent manner. CSE-induced cell death was considered to be apoptotic by observing the typical apoptotic morphological change by AO/EB staining and DNA fragmentation assay. The induction of HepG2 cell death was caused by an induction of apoptosis for the sub-G1 proportion increase, the downregulation of Bcl-2, the upregulation of Bax and p53, and the activation of the caspases-3 and -9 pathways. CONCLUSION: These results clearly demonstrated that CSE was able to inhibit the proliferation of HepG2 cells and cause apoptosis. Moreover, the anticancer effects of CSE were related to the Bcl-2 family pathway and the activation of caspases-3 and -9 in HepG2 cells.