Surface-enhanced Raman spectroscopy (SERS), which utilizes nanogaps between noble-metal nanostructures as hot spots to yield ultrasensitive SERS signals, is an outstanding label-free and straightforward tool for DNA methylation analysis. Herein, a plasmonic gold nanohole array (PGNA) with well-controlled hot spots and an open surface was designed as a SERS substrate for DNA methylation detection. A finite-difference time-domain (FDTD) simulation was first employed to investigate the electric field distributions of the PGNA as a function of the geometric parameters. The plasmonic response was tuned to 785 cm −1 to match the ring breathing vibrational band of cytosine, the intensity change of which was revealed to be a marker of DNA methylation. Then, guided by the FDTD simulation results, the PGNA was fabricated via the electron beam lithography (EBL) technique. The fabricated PGNA had an open and easily accessible surface topology, a SERS enhancement factor of ∼10 6 , and a relative standard deviation (RSD) of 7.1% for 500 repetitions over an area of 20 × 20 μm 2 using 1 μM Rhodamine 6G as the Raman reporter. The fabricated PGNA was further used as a platform for determining DNA methylation. The proposed method exhibited a sensitivity for detecting 1% of methylation changes. Moreover, insight into the dynamic information on methylation events was obtained by combining principal component analysis (PCA) with 2D correlation spectroscopy analysis. Finally, clear discrimination of the different methylation sites, such as 5-methylcytosine and N6-methyladenine, was demonstrated.

In this work, methylammonium lead trichloride (CH3NH3PbCl3) perovskite thin films were fabricated via a two-step spin coating and solvent-vapor-assisted thermal annealing method under low temperature. The films exhibited cubic crystalline structure and pinhole-free morphologies.The possible charge traps were investigated via the analysis of photoluminescence (PL) spectra of perovskite films prepared with different lead chloride (PbCl2) precursor concentrations while maintaining the same concentration of methylammonium chloride (CH3NH3Cl). Prototypical ultraviolet (UV) photodetectors with the structure of ITO/CH3NH3PbCl3/Poly (triaryl amine) (PTAA)/Al were fabricated and showed low dark current density 1.60 × 10 -5 mA/cm 2 under -1 V reverse bias, strong photoresponse in 300-400 nm region, and a high UV-visible rejection ratio up to 500 under 0 or -0.5 V bias. All the results demonstrated that low-temperature solution-processed CH3NH3PbCl3 perovskite thin films offer a great potential for making flexible, lightweight visible-blind UV-A photodetectors.

Lightweight and flexible ultraviolet (UV) photodetectors (PDs) have wide applications and have attracted more attention. PDs using organic and inorganic nanocomposites as active layers with a photodiode configuration could achieve photomultiplication and narrowband photoresponse via the control of microstructure and thickness of active layers. Here, we fabricated flexible UV PDs on indium tin oxide-coated poly(ethylene terephthalate) substrates with a nanocomposite active layer composed of ZnO nanoparticles blended with a wide band gap conjugated polymer, poly[(9,9-dioctylfluorenyl-2,7-diyl)- alt- co-(bithiophene)] (F8T2). As a result of the wavelength-dependent penetration depth of light in the active layer, the fabricated flexible UV PDs showed two narrow response peaks at 360 and 510 nm under reverse biases in the external quantum efficiency (EQE) spectra with full width at half maximum (FWHM) less than 20 nm. Both responses exhibited greater than 100% EQE, indicating a photomultiplication effect, whereas the UV response at 360 nm was 10 times stronger under -15 V bias. The fabricated flexible UV PDs were bent under both tensile and compressive stress to a curvature of 2.1 cm, each with 50 repetitions. The peak specific detectivity ( D*) only decreased by about 5% in total, the FWHM was well retained below 20 nm and the response speed remained almost constant after two types of bending, demonstrating mechanical flexibility and photoresponse stability of the fabricated flexible UV PDs. The photodiode configuration with nanocomposite active layers offers a promising route to make flexible and conformable narrowband, photomultiplication-type photodetectors for modern applications.

Csx(MA0.17FA0.83)1−xPb1−ySny(I0.83Br0.17)3 perovskites with cubic-phase morphologies were deployed in solar cells, achieving high efficiencies and improved stability for high Sn-containing devices.

Narrowband ultraviolet (UV) photodetectors are highly desired in multiple areas. Photodetectors based on organic−inorganic nanocomposites offer high sensitivity, widely adjustable response range, light weight, and lowtemperature solution processibility. However, the broad absorption range of organic and inorganic semiconductor materials makes it difficult to achieve a narrowband detection feature for nanocomposite photodetectors. In this work, nanocomposite thin films containing the wide band gap conjugated polymer poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(bithiophene)] (F8T2) blended with wide band gap ZnO nanoparticles (NPs) serve as the active layers of the photodetectors. Narrowband UV photodetectors with high gain and low driving voltage are demonstrated by adopting a symmetric device structure, controlling the active layer composition and microstructure, and manipulating the light penetration depth in the active layer. The fabricated photodetector exhibits a high external quantum efficiency of 782% at 358 nm under a low forward bias of 3 V with the full-width at halfmaximum of 16 nm. Combined with a low dark current, a high specific detectivity of 8.45 × 10 12 Jones is achieved. The impacts of the F8T2:ZnO NPs weight ratio and the device structure on the UV-selectivity and the device performance are investigated and discussed. Our method offers a pathway to design and fabricate narrowband UV photodetectors.

Organic-inorganic hybrid ultraviolet photodetectors with tunable spectral response are desirable for many different applications. In this work, we blended poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) with ZnO nanoparticles in weight ratios of 1 : 1 and 2 : 1 to create charge traps within the active layers for devices with the conventional structure ITO/PEDOT : PSS/PTAA : ZnO/BCP/Al. Thin (150-200 nm) and thick (1400-1900 nm) active layers were employed to utilize charge collection narrowing (CCN). Both thickness and composition of the active layer impacted the spectral tunability of the photoresponse. A single narrow response peak centered at 420 nm (the PTAA absorption edge) with a full width at half maximum of 12 nm was achieved from the device with a 1900 nm active layer and PTAA : ZnO weight ratio of 1 : 1. Decreasing the active layer thickness to 150 nm resulted in a broad spectral response between 320-420 nm with an external quantum efficiency (EQE) value of 295% under 350 nm illumination and a -1 V bias, exhibiting photomultiplication via charge trapping and injection even at small reverse biases. Increasing the weight ratio of PTAA : ZnO to 2 : 1 lowered both the dark current and photocurrent, eliminated photomultiplication in the thin device, and diminished the efficacy of CCN to narrow the spectral photoresponse in the thick device. Transfer matrix method (TMM) and 3-dimensional finite-difference time-domain (3D-FDTD) simulations were performed to understand the impact of thickness and composition of the active layer on the spectral response of UV photodetectors in terms of exciton generation rate and electric field distribution within the devices.

Epigenetic modifications of DNA are known to modulate gene activity and expression and are believed to result in genetic diseases, such as cancer. Four modified cytosines were discovered in mammalian genomes: 5-methycytoine (5mC), 5hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5carboxycytosine (5caC). They are regarded as DNA epigenetic markers and play key roles in the regulation of the dynamic balance between DNA methylation and demethylation. Although detection approaches toward 5mC are ubiquitous, few assays have reported the simultaneous determination of all four modified cytosines as well as monitoring of their dynamic alterations. Here, we developed a label-free surface enhanced Raman spectroscopy (SERS)-based method for directly sensing the four DNA modifications by using a plasmonic gold nanohole array (PGNA) with well-controlled hot spots and an open surface as the substrate. This method is based on identifying SERS spectral features resulting from DNA base modifications.Our study shows that 5mC, 5hmC, 5fC, and 5caC exhibit distinct Raman spectroscopic signatures at 785, 660, 1450, and 1680 cm −1 , respectively. Moreover, the developed method can be used for tracking of the dynamic alterations among these four modified cytosines in DNA mediated by the ten-eleven translocation (TET) protein. The dynamic stepwise conversion from 5mC into 5hmC, 5fC, and 5caC is further demonstrated to be a typical three-step consecutive reaction with rate constants of 0.6, 0.25, and 0.15 min −1 , respectively, which has not been achieved before via a SERS-based method.

Poly(3,:poly(styrene sulfonate) (PEDOT:PSS) has been widely used as a hole-conducting polymer in many optoelectronic devices including perovskite solar cells. However, its electrical and surface properties are not well controlled during the conventional ambient annealing. Herein, we apply the solvent posttreatments, including toluene vapor annealing and ethylene glycol (EG) washing, to modify not only the electrical conductivity and work function but also, importantly, the surface composition and morphology of PEDOT:PSS thin films. We show that annealing PEDOT:PSS films in a nonpolar toluene vapor environment results in a slightly enhanced electrical conductivity and increased work function while maintaining the surface composition and morphology. The CH 3 NH 3 PbI 3 perovskite solar cells using the toluene vapor-annealed PEDOT:PSS hole transporting layers (HTLs) yield a 31.8% increase in power conversion efficiency (PCE) from the control devices with the ambient conditionannealed PEDOT:PSS HTLs. All photovoltaic parameters are increased because of reduced trap states at the perovskite/HTL interface, as well as efficient and balanced charge generation, transport, and extraction rates. In contrast, washing PEDOT:PSS films with the polar EG solvent removes the PSS on the surface, increases the surface roughness, and dramatically increases the electrical conductivity by 5 orders of magnitude but slightly decreases the work function. Consequently, the CH 3 NH 3 PbI 3 perovskite solar cells with EG-washed PEDOT:PSS HTLs result in a 28.6% decrease in PCE from the control devices because of the increased trap states at the perovskite/HTL interface, which leads to an inefficient hole extraction. The charge accumulation at the perovskite/HTL interface also reflects in a serious hysteresis of J−V curves in the reversed bias region. This work highlights the importance of controlling both electronic and surface properties of PEDOT:PSS HTLs for the improvement of perovskite solar cell performance.