Search Results (65)

Organic photodetectors (OPDs) offer considerable promise for low-power, solution-processable biosensing and imaging applications; however, their performance remains limited by spectral mismatch and interfacial trap states. In this study, a highly sensitive polymer photodiode was developed via trace incorporation (0.8 wt%) of InP/ZnSe/ZnS quantum dots (QDs) into a PTB7-Th:PC₇₁BM bulk heterojunction (BHJ) matrix. This QD doping approach enhanced the external quantum efficiency (EQE) across the 540–660 nm range and suppressed the dark current density at −2 V by passivating interface trap states. Despite a slight decrease in optical absorption at the optimized composition, the internal quantum efficiency (IQE) increased significantly from ~80% to nearly 95% resulting in a net EQE improvement. This suggests that QD incorporation improved charge transport without compromising charge separation efficiency. As a result, the device achieved a specific detectivity (D*) of 1.8 × 10¹³ Jones, representing a 93% improvement over binary BHJs, along with an ultra-low dark current density of 7.76 × 10⁻¹⁰ A/cm². Excessive QD loading, however, led to optical losses and increased dark current, underscoring the need for precise compositional control. Furthermore, the enhanced detectivity led to a 4 dB improvement in the signal-to-noise ratio (SNR) of photoplethysmography (PPG) signals in the target wavelength range, enabling more reliable biophotonic sensing without increased power consumption. This work demonstrates that QD-based spectral and interfacial engineering offers an effective and scalable route for advancing the performance of OPDs, with broad applicability to low-power biosensors and high-resolution polymer–QD imaging systems. Full article

In this study, we analysed cocoa (a dried and fully fermented seed of Theobroma cacao L.) from two Amazonian cultivars and a commercial sample of the Amazonian variety EETP801, grown under sustainable organic conditions, in comparison to CCN51 cocoa grown on a neighbouring commercial farm using standard practises and a European commercial cacao powdered beverage. The overall metabolite profile of the 70% aq acetone sample cocoa extracts was analysed using high-performance TLC analyses (HPTLC), and the xanthine alkaloids were analysed using quantitative liquid chromatography–UV photodiode array (HPLC-DAD) analyses. The volatile fraction in the headspace of the freshly ground cocoa was subjected to solid phase micro-extraction and analysed by gas chromatography–mass spectrometry (HS-SPME/GC-MS). Total polyphenol content was determined by the Folin–Ciocalteu method. Despite the reduced production of cocoa by the EETP801 cultivar in comparison with the CCN51 cultivar, the obtained produce is significantly richer in theobromine (130 mg vs. 170 mg per g of cacao), with CCN51 having a double concentration of theophylline (12.6 vs. 6.5 mg per g of cacao). Qualitatively, the two Amazonian cocoa samples had a similar polyphenolic composition (per the HPTLC fingerprint). HS-SPME/GC-MS analyses revealed that all the samples show a spontaneous emission profile mainly rich in non-terpene derivatives, of which hydrocarbons and pyrazines are the most abundant groups. The most represented volatile organic compound is n-tridecane for both EETP801 and CCN51. The variability in the artisan fermentation and roasting processes influenced certain aspects of the volatile composition as reflected by the trimethyl pyrazine/tetramethyl pyrazine ratio, which was zero in EETP-801 and lower than 1 in CCN51. Acetic acid was absent in CCN51 but significant (c.a. 5.5.%) in EETP801 and the commercial samples. The cultivar EETP801 is a viable option for a more ecologically conscious sector of the cocoa beverages consumer group. Full article

As human life expectancy continues to rise, managing age-related diseases and preserving health in later years remain significant challenges. Consequently, there is a growing demand for strategies that enhance both the quality and the duration of life. Interventions that promote longevity, particularly those derived from natural sources, are popular for their potential to address age-related health concerns. Adaptogens—herbs, roots, and mushrooms—are valued in food science and nutrition for their ability to enhance resilience and overall well-being. Among these, Rhaponticum carthamoides (Willd.) Iljin, known as maral root (Russian leuzea), holds a prominent place in Siberian traditional medicine. The root extract, abundant in bioactive compounds such as flavonoids and phytoecdysteroids, is reputed for reducing fatigue, boosting strength, and offering immunomodulatory benefits. However, the effects of the plant extract on lifespan and age-related decline remains poorly studied. This study investigates the effect of maral root extract and phytoecdysteroids—ecdysterone, ponasterone, and turkesterone—on aging using Caenorhabditis elegans as a model organism. A sensitive liquid chromatography method with photodiode array detection was developed and validated to quantify the phytoecdysteroids in the extract. Behavioural and stress-response assays revealed that maral root not only extends lifespan but also significantly enhanced healthspan, stress resilience, and fitness in the nematodes. Additionally, treatment with ecdysterone, the most abundant compound in the root extract, improved healthspan by enhancing stress response. These findings underscore the potential of maral root as a natural adaptogen to mitigate age-related decline, providing valuable insights into natural longevity interventions. Full article

Optical techniques to study neuronal activity have greatly advanced the field of neuroscience over recent decades. Multichannel silicon-based recording probes combined with optical fibers allow for simultaneous recording and manipulation of neuronal activity that underpins cognitive processes and behavior. The recent development of neural probes incorporating organic light-emitting diodes (OLEDs) and photodiode-based organic photodetectors (OPDs) offer additional advantages of biocompatibility, ultra-small footprint, multifunctionality, and low cost. These developments are ushering in a new generation of devices that are ideal for the interrogation of neuronal activity in vitro and in vivo. In this review, we discuss recent progress in OLED- and OPD-based neural probes, their applications in the optical control of neuronal function, and current challenges and prospects for the future. Full article

Palladium phthalocyanine (PdPc) and palladium phthalocyanine integrated with tin–zinc oxide (PdPc:SnZnO) were prepared using a simple chemical approach, and their structural and morphological properties were identified using X-ray diffraction, energy dispersive X-ray analysis, scanning electron microscopy, and transmission electron microscopy techniques. The PdPc:SnZnO nanohybrid revealed a polycrystalline structure combining n-type metal oxide SnZnO nanoparticles with p-type organic PdPc molecules. The surface morphology exhibited wrinkled nanofibers decorated with tiny spheres and had a large aspect ratio. The thin film revealed significant optical absorption within the ultraviolet and visible spectra, with narrow band gaps measured at 1.52 eV and 2.60 eV. The electronic characteristics of Al/n-Si/PdPc/Ag and Al/n-Si/PdPc:SnZnO/Ag Schottky diodes were investigated using the current–voltage dependence in both the dark conditions and under illumination. The photodiodes displayed non-ideal behavior with an ideality factor greater than unity. The hybrid diode showed considerably high rectification ratio of 899, quite a low potential barrier, substantial specific photodetectivity, and high enough quantum efficiency, found to be influenced by dopant atoms and the unique topological architecture of the nanohybrid. The capacitance/conductance–voltage dependence measurements revealed the influence of alternative current signals on trapped centers at the interface state, leading to an increase in charge carrier density. Full article

Accurate pH sensing is essential for the effective physiological control of the culture media in organ-on-a-chip (OoC) systems. This work proposes a miniaturized optical detection system, based on optical transmittance, for pH level quantification of the EGM™-2 Endothelial Cell Growth Medium-2 BulletKit™ culture medium. Firstly, using a commercial spectrophotometric setup, a set of wavelengths (500, 560, and 600 nm) was selected, as these wavelengths assure distinctive slope variations for the different pH levels. Then, a current-to-frequency converter, based on a low-power Schmitt trigger model with a voltage enhancer, was proposed as the readout electronics and simulated in Cadence Tools using UMC L180 MM/RF technology. A resolution of 0.002 nA was achieved in the linear range of 30 pA to 3800 nA. A miniaturized system composed of a CMOS n-well/p-substrate photodiode and a polydimethilsiloxane (PDMS) microchannel for the culture media substrate was experimentally tested. For a pH range from 6.6 to 6.2, the results clearly demonstrate a magnitude shift of the slope signal, which becomes negative in basic media and positive in acidic media. Additionally, in the 500–560 nm spectral range, the amplitude of the slopes increases for both basic and acidic culture media. In the 560–600 nm range, the slope decreases progressively as the pH of the medium lowers. This miniaturized system was able to quantify the pH of the culture medium, showing potential to be integrated into an organ-on-a-chip device. Full article

We investigate the inorganic/organic hybrid vertical phototransistor (VPT) by integrating an atomic layer deposition-processed ZnO (ALD-ZnO) transistor with a prototype poly(3-hexylthiophene):[6,6]-phenyl-C₆₁-butyric acid methyl ester (P3HT:PC₆₁BM) blend organic photodiode (OPD) based on an encapsulated source electrode geometry, and discuss the device mechanism. Our preliminary studies on reference P3HT:PC₆₁BM OPDs show non-ohmic electron injection between the ALD-ZnO and P3HT:PC₆₁BM layers. However, the ALD-ZnO layer enables the accumulation of photogenerated holes under negative bias, which facilitates electron injection upon illumination and thereby enhances the external quantum efficiency (EQE). This mechanism underpins the photoresponse in the VPT. Furthermore, we demonstrate that the gate field in the VPT effectively modulates electron injection from the ALD-ZnO layer to the top OPD, resulting in the VPT operating as a non-ohmic OPD in the OFF state and as an ohmic OPD in the ON state. Benefiting from the unique transistor geometry and gate modulation capability, this hybrid VPT can achieve an EQE of 45,917%, a responsivity of 197 A/W, and a specific detectivity of 3.4 × 10¹² Jones under 532 nm illumination and low drain-source voltage (V_ds = 3 V) conditions. This transistor geometry also facilitates integration with various OPDs and the miniaturization of the ZnO channel area, offering an ideal basis for the development of highly efficient VPTs and high-resolution image sensors. Full article

Phototransistors are three-terminal photodetectors that usually have a higher photocurrent gain than photodiodes due to the amplification of the gate electrode. In this work, a broad spectral phototransistor based on copper phthalocyanine (CuPc) and a Cs₃Bi₂I₉ (CBI) heterojunction is fabricated by the full vacuum evaporation method. Due to the complementary UV–visible absorption of CuPc and CBI, the device exhibits superior performance under three different types of visible light illumination. The experimental results show that the structure of the organic/perovskite heterojunction active layer has the characteristics of good compatibility and a simple process. Meanwhile, by utilizing the superior light-absorption characteristics of perovskite materials and the strong exciton dissociation efficiency of a hetero-type heterojunction interface, the CuPc/CBI-PT exhibits a higher photoresponsivity, photosensitivity, specific detection rate, and lower operating voltage than the CuPc reference device. The stability test shows that the CuPc/CBI-PT can still obtain a 0.73 A/W photoresponsivity under 660 nm light illumination after being stored in the air for 360 h without any packaging. This indicates that the organic/perovskite heterojunction PT may be a good choice for the preparation of high-performance photodetectors. Full article

The resolution of Si complementary metal–oxide–semiconductor field-effect transistor (C-MOSFET) image sensors (CISs) has been intensively enhanced to follow the technological revolution of smartphones, AI devices, autonomous cars, robots, and drones, approaching the physical and material limits of a resolution increase in conventional Si CISs because of the low quantum efficiency (i.e., ~40%) and aperture ratio (i.e., ~60%). As a novel solution, a hybrid organic–Si image sensor was developed by implementing B, G, and R organic photodiodes on four n-MOSFETs for photocurrent sensing. Photosensitive organic donor and acceptor materials were designed with cost-effective small molecules, i.e., the B, G, and R donor and acceptor small molecules were Coumarin6 and C_60, DMQA and MePTC, and ZnPc and TiOPc, respectively. The output voltage sensing margins (i.e., photocurrent signal difference) of the hybrid organic–Si B, G, and R image sensor pixels presented results 17, 11, and 37% higher than those of conventional Si CISs. In addition, the hybrid organic–Si B, G, and R image sensor pixels could achieve an ideal aperture ratio (i.e., ~100%) compared with a Si CIS pixel using the backside illumination process (i.e., ~60%). Moreover, they may display a lower fabrication cost than image sensors because of the simple image sensor structure (i.e., hybrid organic–Si photodiode with four n-MOSFETs). Full article

Deep defects in the long-wave infrared (LWIR) HgCdTe heterostructure photodiode were measured via deep-level transient spectroscopy (DLTS) and photoluminescence (PL). The n⁺-P⁺-π-N⁺ photodiode structure was grown by following the metal–organic chemical vapor deposition (MOCVD) technique on a GaAs substrate. DLTS has revealed two defects: one electron trap with an activation energy value of 252 meV below the conduction band edge, located in the low n-type-doped transient layer at the π-N⁺ interface, and a second hole trap with an activation energy value of 89 meV above the valence band edge, located in the π absorber. The latter was interpreted as an isolated point defect, most probably associated with mercury vacancies (V_Hg). Numerical calculations applied to the experimental data showed that this V_Hg hole trap is the main cause of increased dark currents in the LWIR photodiode. The determined specific parameters of this trap were the capture cross-section for the holes of σ_p = 10⁻¹⁶–4 × 10⁻¹⁵ cm² and the trap concentration of N_T = 3–4 × 10¹⁴ cm⁻³. PL measurements confirmed that the trap lies approximately 83–89 meV above the valence band edge and its location. Full article

The cooling requirement for long-wave infrared detectors still creates significant limitations to their functionality. The phenomenon of minority-carrier exclusion and extraction in narrow-gap semiconductors has been intensively studied for over three decades and used to increase the operating temperatures of devices. Decreasing free carrier concentrations below equilibrium values by a stationary non-equilibrium depletion of the device absorber leads to a suppression of Auger generation. In this paper, we focus on analyzing exclusion and extraction effects separately, based on experimental and theoretical results for a HgCdTe photodiode. To carry out an experiment, the n⁺-P⁺-π-N⁺ heterostructure was grown by metal organic chemical vapor deposition on CdTe-buffered GaAs substrate. In order to separate the extraction and exclusive junctions, three different devices were evaluated: (1) a detector etched through the entire n⁺-P⁺-π-N⁺ heterostructure, (2) a detector made of the P⁺-π photoconductive junction and (3) a detector made of the π-N⁺ photodiode junction. For each device, the dark current density–voltage characteristics were measured at a high-temperature range, from 195 K to 300 K. Next, the carrier concentration distribution across the entire heterostructure and individual junctions was calculated using the APSYS simulation program. It was shown that when the n⁺-P⁺-π-N⁺ photodiode is reverse biased, the electron concentration in the π absorber drops below its thermal equilibrium value, due to the exclusion effect at the P⁺-π junction and the extraction effect at the π-N⁺ junction. To maintain the charge neutrality, the hole concentration is also reduced below the equilibrium value and reaches the absorber doping level (N_A), leading to the Auger generation rate’s reduction by a factor of 2n_i/N_A, where n_i is the intrinsic carrier concentration. Our experiment conducted for three separate detectors showed that the exclusion P⁺-π photoconductive junction has the most significant effect on the Auger suppression—the majority of the hole concentration drops to the doping level not only at the P⁺-π interface but also deep inside the π absorber. Full article

The vacuum process using small molecule-based organic materials to make organic photodiodes (OPDIs) will provide many promising features, such as well-defined molecular structure, large scalability, process repeatability, and good compatibility for CMOS integration, compared to the widely used Solution process. We present the performance of planar heterojunction OPDIs based on pentacene as the electron donor and C60 as the electron acceptor. In these devices, MoO₃ and BCP interfacial layers were interlaced between the electrodes and the active layer as the electron- and hole-blocking layer, respectively. Typically, BCP played a good role in suppressing the dark current by two orders higher than that without that layer. These devices showed a significant dependence of the performance on the thickness of the pentacene. In particular, with the pentacene thickness of 25 nm, an external quantum efficiency at the 360 nm wavelength according to the peak absorption of C60 was enhanced by 1.5 times due to a cavity effect, compared to that of the non-cavity device. This work shows the importance of a vacuum processing approach based on small molecules for OPDIs, and the possibility of improving the performance via the optimization of the device architecture. Full article

The selection of the π-conjugation spacers in semi-conducting polymer backbone is one of the important factors for determining the optoelectrical and morphological properties in organic photodiodes. To study the effects of π-conjugation spacers in donor–acceptor (D-A)-type alternating copolymers on their device performances in all-polymer-based photodiodes (all-PPDs), a series of diketopyrrolopyrrole (DPP)-based copolymers as polymer donors (P_Ds) were designed and synthesized. In detail, three different π-conjugation spacers, thiophene (T for P1), thienothiophene (TT for P2), and bithiophene (BT for P3), were incorporated into the DPP-based copolymer structures. Interestingly, all-PPDs based on the series of P1–P3 as P_Ds and N2200 as a polymer acceptor (P_A) exhibited totally distinct device performances in terms of external quantum efficiency (EQE), dark current density (J_D), and ideal detectivity (D*). The P1-based device showed suppressed J_D (6.1 × 10⁻¹¹ A/cm² at −1 V) compared to those of the P2- and P3-based devices due to the lower lying of the highest occupied molecular orbital (HOMO) level of P1. However, the P3-based all-PPD showed higher EQE (16% at 630 nm wavelength and −1 V) compared to those of the P1- and P2-based devices. And, it mainly originated from the better molecular packing and final blend film morphology, as confirmed by morphological analyses. Full article

Water pollution is a critical issue since it can severely affect health and the environment. The purpose of the study is to develop a portable spectrometer (ESP32-based spectrometer) to detect chemical contaminants in irrigation water by observing the light absorbance of contaminants. ESP32 and a light sensor (photodiode) were respectively, used as the main controller and detector of the portable spectrometer. It was developed based on optical dispersion and Beer–Lambert law theory. The light absorbance of different types of contaminants was displayed in a Blynk application for real-time monitoring. The samples were also tested using a lab-based spectroscopy method, ultraviolet-visible (UV-Vis) spectrometer. The spectral range of the measurement is from 350 nm to 700 nm and the standard error of the ESP32-based spectrometer is from 0.01 to 0.05. Five water samples were tested, consisting of ammonium nitrate, organic pesticide, zinc oxide and two different reservoirs used for irrigation. The absorption peaks of the ammonium nitrate and organic pesticide are 363 nm and 361 nm, respectively. Zinc oxide shows the absorbance peak at 405 nm, whereas both reservoirs show absorbance peaks lie in the region from 300 nm to 370 nm. Therefore, this study shows that different types of contaminants can absorb light only at specific wavelength regions by considering the concentration of samples. The developed ESP32-based spectrometer can be applied for on-site water quality monitoring as it is portable, light, simple and can be monitored in real time using multiple devices. Full article

α-Glucosidase inhibitors are essential in the treatment of diabetes mellitus. Plant-derived drugs are promising sources of new compounds with glucosidase-inhibiting ability. The Geum aleppicum Jacq. and Sibbaldianthe bifurca (L.) Kurtto & T.Erikss. herbs are used in many traditional medical systems to treat diabetes. In this study, metabolites of the G. aleppicum and S. bifurca herbs in active growth, flowering, and fruiting stages were investigated using high-performance liquid chromatography with photodiode array and electrospray ionization triple quadrupole mass spectrometric detection (HPLC-PDA-ESI-tQ-MS/MS). In total, 29 compounds in G. aleppicum and 41 components in S. bifurca were identified including carbohydrates, organic acids, benzoic and ellagic acid derivatives, ellagitannins, flavonoids, and triterpenoids. Gemin A, miquelianin, niga-ichigoside F1, and 3,4-dihydroxybenzoic acid 4-O-glucoside were the dominant compounds in the G. aleppicum herb, while guaiaverin, miquelianin, tellimagrandin II₂, casuarictin, and glucose were prevailing compounds in the S. bifurca herb. On the basis of HPLC activity-based profiling of the G. aleppicum herb extract, the most pronounced inhibition of α-glucosidase was observed for gemin A and quercetin-3-O-glucuronide. The latter compound and quercetin-3-O-arabinoside demonstrated maximal inhibition of α-glucosidase in the S. bifurca herb extract. The obtained results confirm the prospects of using these plant compounds as possible sources of hypoglycemic nutraceuticals. Full article