Detection Wavelength Research Articles

A comprehensive review of analytical strategies for validating RP-HPLC methods of aceclofenac and thiocolchicoside in bulk drug and formulation

This comprehensive review explores the analytical method development and validation of Aceclofenac and Thiocolchicoside bulk drugs and formulations using Reverse Phase High-Performance Liquid Chromatography (RP-HPLC). Aceclofenac, a nonsteroidal anti-inflammatory drug (NSAID), and Thiocolchicoside, a muscle relaxant, are commonly co-formulated for the treatment of pain and inflammation. The review discusses the principles and strategies involved in RP-HPLC method development, emphasizing factors such as stationary phase selection, mobile phase composition, and detection wavelength optimization. Furthermore, it highlights the importance of method validation in pharmaceutical analysis, covering parameters such as specificity, linearity, accuracy, precision, robustness, and system suitability. The literature review section examines previous studies on RP-HPLC methods developed for Aceclofenac and Thiocolchicoside, summarizing key findings and comparing different methodologies. Challenges and limitations encountered during method development and validation are discussed, along with recent advances in RP-HPLC methodology. Finally, the review outlines future research directions and potential applications of RP-HPLC in studying the pharmacokinetics and bioavailability of Aceclofenac and Thiocolchicoside formulations.

A highly sensitive, accurate, and stable method for measuring pectin depolymerase activity

Pectin depolymerase is widely utilized in various industrial sectors. However, the traditional methods for determining its enzymatic activity have limitations, such as cumbersome operations and a significant impact of enzyme solution dilution ratios on activity. The 3-methyl-2-benzothiazolinone hydrazone (MBTH) method can be employed to address these issues, but pectin precipitation and strong background commonly arise in this method. We have successfully overcome these challenges by employing a low-temperature and high-alkaline environment, and further optimized the reagent compositions and detection wavelength to improve the method. Consequently, enzyme hydrolysis follows a zero-order reaction within 60 min, which is helpful for the endpoint measurement of pectinase activity. The developed calibration curve for pectinase concentration and hydrolysis rate demonstrates linearity (R2 = 0.9945) within the range of 2.5–15.8 mU/mL of pectinase. This method exhibits high sensitivity, accuracy, and stability, making it suitable for routine determination of pectin depolymerase activity in research and applications.

Method Development and Validation of Assay of Rilpivirine in Rilpivirine Tablets by RP-HPLC

A method was developed and validated for determining the Assay of Rilpivirine in Rilpivirine Tablets by using WATERS HPLC 2695 with Autosampler, PDA Detector and Empower 3 Software. ACE Excel 3 C18 AR (250 x 4.6 mm, 3 μm) column was used along with a mobile phase combination Acetate Buffer: Methanol: Acetonitrile in ratio 60: 30: 10 % v/v/v. Isocratic flow with flowrate of 1.5 mL/minute, Injection volume 12 mL was employed. Column temperature of 30°C was maintained. Detection wave length of Rilpivirine was 258 nm. Run time was optimised to 5 min based on retention time. The retention time of Rilpivirine was 2.29 minutes. The method was found to be specific, linear with a square of correlation coefficient (R2 ) 1.000, accurate over the concentration range of 25 % to 200 %, precise with % RSD of six samples 1.1 and robust. Thus a simple, quick and economical method was developed and validated.

Sb2Te3–Bi2Te3 Direct Photo–Thermoelectric Mid‐Infrared Detection

AbstractA compact and responsive thermoelectric photodetector is introduced for the mid‐infrared. By resonantly coupling mid‐infrared light to a Sb2Te3‐Bi2Te3 thermoelectric junction, a thermocouple is formed that is directly heated by narrow‐band mid‐infrared radiation. Near‐perfect absorption is achieved at this hot junction through the resonantly enhanced coupling of light to free‐electrons in the Bi2Te3 and Sb2Te3 materials. The fabricated devices operate at 3.6 µm and demonstrate a responsivity of 10.2 V W−1, a specific detectivity of 4.6 × 106 cm Hz1/2 W−1, and a bandwidth in the order of 1 kHz. The optimal detection wavelength can be spectrally tuned by changing the resonant cavity dimensions. This work shows a path toward miniaturized mid‐infrared detectors and spectrometers with high sensitivity, responsivity, and bandwidth. Importantly, the device presented here is ideal for industrial production, which it is hoped will provide wider access to mid‐infrared technologies for chemical sensing, medicine, and security.

On chip control and detection of complex SPP and waveguide modes based on plasmonic interconnect circuits

Abstract Optical interconnects, leveraging surface plasmon modes, are revolutionizing high-performance computing and AI, overcoming the limitations of electrical interconnects in speed, energy efficiency, and miniaturization. These nanoscale photonic circuits integrate on-chip light manipulation and signal conversion, marking significant advancements in optoelectronics and data processing efficiency. Here, we present a novel plasmonic interconnect circuit, by introducing refractive index matching layer, the device supports both pure SPP and different hybrid modes, allowing selective excitation and transmission based on light wavelength and polarization, followed by photocurrent conversion. We optimized the coupling gratings to fine-tune transmission modes around specific near-infrared wavelengths for effective electrical detection. Simulation results align with experimental data, confirming the device’s ability to detect complex optical modes. This advancement broadens the applications of plasmonic interconnects in high-speed, compact optoelectronic and sensor technologies, enabling more versatile nanoscale optical signal processing and transmission.

Analytical quality by design-based stability-indicating high performance liquid chromatography method for the estimation of evogliptin tartrate in bulk and tablet dosage form.

The present study utilized Analytical Quality by Design (AQbD) approach to develop a stability-indicating high-performance liquid chromatography (HPLC) method for estimating evogliptin tartrate using design expert software. The key parameters were methodically optimized, contours were plotted, and stability was evaluated using various forced degradation conditions. Using an Agilent HPLC system with a photo diode array (PDA) detector along with Fortis C18 column (250 × 4.6mm, 5μm) effectively separated the drug from its degradants. The mobile phase used was methanol: water (pH adjusted to 3.0, 76:24; v/v) at 0.8mL/min flow rate. Evogliptin was eluted at 2.98 min, at a detection wavelength of 267 nm. The proposed method was found to be specific, precise, linear and robust. The drug was sensitive to acidic, basic, oxidative, thermal, and photodegradation resolving six degradation products. Thus, the developed AQbD-based stability-indicating HPLC method is applicable in analyzing evogliptin in bulk, tablet dosage form and stability samples.

HPLC-DAD method validation for quantification of dehydroabietic acid and abietic acid in oral spray containing Pinus merkusii heartwood extract and its antibacterial effects on clinically isolated Streptococcus mutans

AbstractPinus merkusii Jungh & De Vries. has become increasingly gathered more attention from researchers because the plant has a range of folk medicinal uses. Heartwood plant is the major source of dehydroabietic acid (DHAA) and abietic acid (AA), which possesses several medicinal properties, such as antiviral, antimicrobial, antiobesity and anti-inflammatory. The research proposed herein a low-cost, fast, specific, uncomplicated, sensitive, precise reverse-phase high-performance liquid chromatography (RP-HPLC). This method was conducted and validated for evaluating an amount of DHAA and AA in ethanol extract and oral spray containing P. merkusii heartwood extract. Additionally, stability and antimicrobial activities against clinically isolated Streptococcus mutans of the oral spray were determined. The separation was achieved on Pursuit 200Å PFP column, 150 × 4.6 mm, particles of 3 µm with a flow rate of 1.0 mL min−1. Methanol and water (70:30 v/v) were used as eluent with an isocratic mode and sample analysis volume was set at 10 µL, at a detection wavelength of 210 and 245 nm. The developed HPLC method for analysis of DHAA and AA showed good linearity with correlation coefficients equal to 1. Moreover, other validation parameters, comprised of accuracy, precision, specificity and detection and quantitation limits of this method displayed excellent reliability, validity and sensitivity. This method could be an interesting alternative for quantitative measurement of P. merkusii heartwood extract, oral spray formulation and other P. merkusii heartwood extract preparations. The result from antibacterial tests suggested that the oral spray containing P. merkusii heartwood extract is able to inhibit the oral pathogens causing dental caries. The oral spray decreased S. mutans population size by about 0.5–2 Log CFU mL−1 at 1–4 h and complete elimination of all bacteria strains within 24 h. This study provides validity for using P. merkusii heartwood extract as an alternative for preventing and treating oral infectious diseases.

Determination of anamorelin concentration in human plasma using a simple high-performance liquid chromatography-ultraviolet detection method.

Anamorelin, a non-peptide ghrelin analog and growth hormone secretagogue, is a novel oral drug used to treat cancer cachexia. Patients with cancer cachexia frequently use several drugs and anamorelin is a substrate of cytochrome P450 (CYP) 3A4; therefore, drug-drug interactions with CYP3A4 inhibitors and inducers pose a clinical problem. In this study, we aimed to determine the concentration of anamorelin in human plasma using a simple high-performance liquid chromatography-ultraviolet (HPLC-UV)-based method. The analysis involved extracting a 200-μL plasma sample and protein precipitation using solid-phase extraction. Anamorelin was isocratically separated using a mobile phase consisting of 0.5% potassium dihydrogen phosphate (pH 4.5) and acetonitrile (61:39, v/v) on a Capcell Pack C18 MG II column (250 mm × 4.6 mm) at a flow rate of 1.0 mL/min and monitored at a detection wavelength of 220 nm. The calibration curve was linear within a plasma concentration range of 12.5-1,500 ng/mL, with a coefficient of determination of 0.9999. The intra- and inter-day coefficients of variation were 0.37-6.71% and 2.05-4.77%, respectively. The accuracy of the assay and recovery were 85.25-112.94% and > 86.58%, respectively. This proposed HPLC-UV method is simple and can be applied in clinical settings.

Analysis of Aspirin (Acetylsalicylic Acid): Development and Validation using RP-HPLC Methods - A Component of Anti-hypertensive Drugs

A precise, sensitive, and focused liquid chromatographic method has been developed to assess the quantity of aspirin in its bulk form. The chromatographic conditions involved utilizing a C-18 column (250 x 4.6 mm, 5 µm particle size) with a mobile phase consisting of water containing 0.1% orthophosphoric acid (v/v) at pH 3.0 and acetonitrile in a ratio of 45:55. The flow rate was set at 1 ml per minute, and the total run time was 20 minutes, with a detection wavelength of 237 nm. The retention time was observed to be 4.01 minutes, and the method exhibited an average recovery percentage of 99.9%. The proposed procedure adhered to the guidelines established by the ICH and is applicable for analyzing aspirin as a standalone bulk drug and in combination with other pharmaceuticals.

Determination of Enantiomeric Impurity in Tegoprazan Drug Substance by HPLC

ABSTRACTTegoprazan is a novel potassium‐competitive acid blocker used for gastroesophageal reflux disease. It is administered as the (S)‐ and (R)‐enantiomers are considered impurities that should be controlled. The objective of this work was to establish a chiral analytical method for the determination of the enantiomeric impurity of tegoprazan in the drug substance by high‐performance liquid chromatography (HPLC). Enantioselective separation was performed on a Chiralpak alpha1‐acid glycoprotein (AGP) column (4.6 mm × 250 mm, 5.0 µm) at 30°C utilizing a mobile phase consisting of 5 mmol L−1 ammonium acetate buffer (pH 6.0) and 2‐propanol (93:7, v/v) at a flow rate of 0.7 mL min−1 with a detection wavelength of 220 nm. The effects of chromatographic conditions, including the type and concentration of organic modifiers, buffer pH, buffer concentration, flow rate, and column temperature, were thoroughly investigated. Under the optimized conditions, the resolution between (S)‐ and (R)‐tegoprazan was greater than 3.0. Moreover, the developed method was validated in terms of linearity, limits of detection (LOD) and quantitation (LOQ), accuracy, precision, and stability. Each enantiomer showed a good linear relationship over the concentration range of 1.0–100 µg mL−1, with the correlation coefficient of 0.9999. The LOD and LOQ were 0.1 and 0.3 µg mL−1, respectively. In addition, the recoveries ranged from 94.10% to 99.39% with a relative standard deviation (RSD) of 1.9%. Application of this proposed method to determine the enantiomeric impurity in tegoprazan drug substance proved satisfactory. The quantitative results were about 2.0%, demonstrating that enantiomeric impurity remained in the tegoprazan drug substance and should be controlled in the quality criteria.

Comparing Gaia, NED and SIMBAD source classifications in nearby galaxies

Abstract Gaia Data Release 3 (DR3) provides the first classifications for the sources in Gaia’s all-sky database. Most Gaia sources are stars in the Milky Way, but DR3 also contains many sources that belong to nearby galaxies, as well as background galaxies and quasars. In this work, we compare the Gaia classifications from the Discrete Source Classifier (CU8-DSC) module to the more detailed and heterogeneous classifications in NED and/or SIMBAD for sources with sky positions within twice the Holmberg radius of nearby galaxies. Matching these catalogues gives approximately 3.2 × 105 unique Gaia matches for 4 × 105 sources over 1040 galaxies (excluding some large Local Group galaxies) in the Local Volume Galaxy catalogue. Matched sources contain a lower fraction of Gaia-classified stars and higher fractions of galaxies and quasars (∼95, 2 and 2 per cent, respectively) than DR3 overall. Considering NED (SIMBAD) classifications as truth values, the balanced accuracy of Gaia classification is 0.80 (0.83): the most common disagreements are literature-classified galaxies Gaia-classified as stars and literature-classified stars Gaia-classified as quasars. Purity (P) and completeness (C) metrics show that agreement between Gaia classification and NED/SIMBAD classification is best for stars (P, C ∼ 0.9), and decreases for quasars (P < 0.3, 0.7 < C < 0.8), galaxies (0.7 < P < 0.8, 0.3 < C < 0.6), white dwarfs (0.04 < P < 0.6, C ∼ 0.6), and binary stars (P, C < 0.1). NED or SIMBAD sources classified only by detection wavelength are most often Gaia-classified as stars, while non-stellar components of galaxies appear in all Gaia classes.

Efficient Green Solvent Extraction and Bioassay Studies of Favipiravir in Rat Dried Blood Spots Using Ionic Liquid-Based Dispersive Liquid-Liquid Microextraction (IL-DLLME) Coupled with HPLC-PDA: Application to Bioequivalence Studies

Background: Favipiravir is an antiviral drug having pyrazine group moiety. It is a reliable and an efficient green solvent, and a highly recoverable bio-sampling method is required for it. It is widely used in COVID-19 treatment for the prevention of the spread of viral infections in the body Objective: This proposed green solvent (ionic liquid)-based bioassay study aimed to quantify favipiravir in rat-dried blood spots using Dispersive Liquid-liquid Microextraction (IL-DLLME). Methods: The proposed bioassay separation was achieved through an isocratic elution mode using a hybrid silica-based ODS column (250 × 4.6 mm; 5 μm), a column temperature of 25°C, an injection volume of 10 μL, a flow rate of 1.0 mL/min, and a detector wavelength set at 310 nm. The run time was less than 10 minutes. Mobile phase was delivered with acetonitrile, methanol, and 10 mM Na2HPO4 at pH 4.0 ± 0.5, (15: 20: 65, v/v/v). In a microtube, 50 mL of Ionic Liquid (IL), 500 μL of disperser ACN, 50 μL of 10% NaCl, and IS (20 ng mL-1) were added to perform the Dried Blood Spot (DBS) sample extraction methodology. The advantages of the proposed methodology have been found to include minimum hematocrit effect and an adequate blood volume for testing, easy transportation, and significant extraction recovery. The sample analysis has been carried out using HPLC-PDA with oseltamivir used as an internal standard. Results: We have investigated the important variables, i.e., salt concentration (10% NaCl, analyte recovery being higher) and disperser solvent [50μL of BMIHP plus 500 μL of ACN (v/v) yielding the highest recovery], in the extraction process. Extraction Recovery (ER) and Enrichment Factor (EF) were also evaluated using the IL-DLLME method. The calibration curve examined a range of 0.5-150 μg/mL, with a lower Limit of Quantification (LOQ) being 0.5 μg/mL in QC as well as calibration samples, respectively. Conclusion: Significant bioanalytical validation has been performed and all the parameters have been evaluated systematically as per bioanalytical method validation protocols, i.e., US FDA- 2018 guidelines. The following analytical parameters have been covered: standard curve, limit of quantification, range, recovery, stability, accuracy, precision, sensitivity, ER, EF, and selectivity. The developed bioassay method has been successfully applied in the pharmacokinetic studies of rats and successfully applied in bulk drugs.

A Validated Chiral Chromatography Method for Enantiomeric Separation of Pomalidomide in Human Plasma.

In the present work, new chiral stationary phase high-performance liquid chromatography (CSP-HPLC) method was established and validated for the quantification of pomalidomide (PMD) enantiomers in human plasma. The chromatographic enantiomeric separation was achieved on a Daicel-CSP, Chiralpack IA 4.6 × 250mm, 5μm; because of its advantages of high degree of retention, high resolution capacity, better reproducibility, ability to produce lower back pressure and low degree of tailing. The mobile phase was maintained as methanol: glacial acetic acid (499.50ml:50μL). Ultraviolet wavelength for detection was 220nm. PMD enantiomer-I and enantiomer-II were separated at 8.83 and 15.34min, respectively. Limit of detection and limit of quantification for each enantiomer and the calibration curve of standard PMD was linear in range between 10-5,000ngmL-1. The method was validated according to The International Council for Harmonisation of Technical Requirements of Pharmaceuticals for Human Use (ICH(Q2R1)) specific guidelines. We found no interference peak with PMD chromatogram obtained. This is a simple, reliable and specific method for detection and quantification of enantiomer of PMD in human plasma sample.

Multi-dimensional optical information acquisition based on a misaligned unipolar barrier photodetector

Acquiring multi-dimensional optical information, such as intensity, spectrum, polarization, and phase, can significantly enhance the performance of photodetectors. Incorporating these dimensions allows for improved image contrast, enhanced recognition capabilities, reduced interference, and better adaptation to complex environments. However, the challenge lies in obtaining these dimensions on a single photodetector. Here we propose a misaligned unipolar barrier photodetector based on van der Waals heterojunction to address this issue. This structure enables spectral detection by switching between two absorbing layers with different cut-off wavelengths for dual-band detection. For polarization detection, anisotropic semiconductors like black phosphorus and black arsenic phosphorus inherently possess polarization-detection capabilities without additional complex elements. By manipulating the crystal direction of these materials during heterojunction fabrication, the device becomes sensitive to incident light at different polarization angles. This research showcases the potential of the misaligned unipolar barrier photodetector in capturing multi-dimensional optical information, paving the way for next-generation photodetectors.

Separation of iodate, bromide, nitrite, nitrate, and iodide in seawater by ion chromatography using 1-aminoundecyl group chemically bonded silica columns.

The separation and detection of six common inorganic anions (iodate (IO3-), bromate (BrO3-), bromide (Br-), nitrite (NO2-), nitrate (NO3-), and iodide (I-)) in pure water and 35 ‰ artificial seawater were examined by ion chromatography (IC). As packing materials of separation columns, 1-aminoundecyl group chemically bonded silica (AUS) gels were prepared. Separation of the anions in pure water was achieved using separation columns (150mm × 4.6mm i.d.) packed with the AUS gels, 0.1M NaCl + 5mM phosphate buffer (pH 4.5) as eluent, and a UV detector (wavelength 225nm). The anions in artificial seawater were separated and detected with a 300mm-long column without interferences by matrix anions such as chloride (Cl-) and sulfate (SO42-). The stationary phases have high-capacity anion-exchange/hydrophilic/hydrophobic interaction mixed-modes. The IC system was applied to five inorganic anions, IO3-, Br-, NO2-, NO3-, and I- in seawater of the Seto-Inland Sea, Japan. The detection limits (DLs, S/N = 3) were 11µgL-1 (IO3-), 93 (Br-), 1.3 (NO2-), 1.4 (NO3-), and 1.1 (I-) for a 100-µL sample injection.

Simultaneous determination of Rosuvastatin calcium and Bempedoic acid in fixed-dose combination pharmaceutical dosage forms using RP-HPLC method

A precise, simple, and, accurate method for simultaneous estimation of Rosuvastatin calcium and Bempedoic acid was developed by Reversed phase High-Performance Liquid Chromatographic (RP-HPLC). The validation of the developed method is done as per ICH guidelines. The method was developed on Waters HPLC using a Kromasil 100-5-C18 (4.6 × 250 mm) column with a detection wavelength of 220 nm. The mobile phase consists of 0.1 % OPA in water: Acetonitrile (50:50 v/v). The retention time for Rosuvastatin calcium and Bempedoic acid was found as 5.4 and 10.7 min respectively. The linearity range was established between 10.0–100.0 µg/ml for Rosuvastatin calcium and 45.0–450.0 µg/ml for Bempedoic acid. The correlation coefficients (r2 values) for Rosuvastatin calcium and Bempedoic Acid were 0.9985 and 0.9988 respectively, indicating a strong concentration–response relationship. The method was found to be specific as there was no interference with the peak of Rosuvastatin calcium and Bempedoic acid in presence of excipients. The % Recovery of the method was found to be 98.64 %, 99.35 %, and 98.27 % for Rosuvastatin calcium and 99.11 %, 99.16 %, and 99.46 % for Bempedoic Acid. Therefore, the method has good trueness. Repeatability analysis of 6 samples revealed %RSD values of 0.92 % and 1.41 % for Rosuvastatin calcium and Bempedoic Acid respectively. The method is precise as the mean %RSD for Intraday studies of Rosuvastatin calcium and Bempedoic acid was 0.6064 % and 0.5289 % respectively while the Interday studies were 0.8763 % and 0.4955 % respectively. The LOD and LOQ for Rosuvastatin calcium are 0.054 µg/ml and 0.163 µg/ml and for Bempedoic acid are 0.127 µg/ml and 0.387 µg/ml respectively. Also, the method is robust as there was no significant change in result upon changing the method parameter. The developed method is environment friendly and is suitable for the quality control analysis of Rosuvastatin calcium and Bempedoic acid either alone or in combination.

(Invited) Photoluminescence Dynamics in PbS/CdS Core/Shell Nanocrystal Films: Carrier Recombination and Energy Transfer

Colloidal semiconductor nanocrystals (NCs) exhibit highly controllable size-dependent optical properties due to the quantum confinement effect. Among other semiconductor NCs, the lead chalcogenides, especially PbS, are one of the most studied and promising NC systems. They are the material of choice for studies of fundamental phenomena as well as for the development of solution processed infrared optoelectronic devices including LEDs, lasers, solar cells, and photodetectors. Compared to organically passivated NCs, the core-shell approach (more specifically PbS/CdS core-shell NCs) offers not only the improved stability and higher photoluminescence (PL) quantum efficiency but also an opportunity of the core/shell interface nano-engineering resulting in suppression of Auger recombination, reduction of the exciton radiative lifetime and an improved lasing threshold. However, despite more than a decade of detailed studies there are conflicting reports on PL dynamics in PbS/CdS core-shell NCs, and there is no accepted model explaining the observed PL lifetimes ranging from hundred nanoseconds to tens of microseconds. In this work we use time-resolved PL measurements and demonstrate that low-temperature PL dynamics in PbS/CdS core shell NCs show strong dependence on the PL detection wavelengths. The presented experimental results allow us to distinguish between processes of energy transfer and exciton recombination. We propose a model, which considers energy transfer between NCs and various mechanisms of exciton recombination (non-radiative, radiative, spin-flip, diffusion limited, etc.).

(Invited) Development of Ag- and Sn-Based Colloidal Quantum Dots for Near Infrared Photodetection

Low-cost photodetectors with sensitivity in the second near-infrared window (NIR-II, 1000–1700 nm) are highly demanded. Recently, we made the first demonstration of an Ag2Se colloidal quantum dots (QDs) photodiode with sensitivity up to 1200 nm. By employing secondary phosphine to elevate the precursor reactivity, the Ag2Se QDs with a distinct excitonic absorption peak was achieved. These nanocrystals were deposited from solution into a mesoporous TiO2 scaffold to increase the light absorption and charge separation and reduce the exciton diffusion length. By incorporating a suitable hole-transporting layer between the active layer and Ag anode, the resulting devices showed a responsivity of 4.17 mA/W at 1200 nm.1 Also, Ag2Te QDs are excellent for advancing the detection wavelength. Their synthesis with desired particle sizes, narrow size distribution and high photoluminescence quantum yield (PL QY) is challenging. We systematically investigate critical parameters affecting the synthesis in an organic phase. It shows that high Ag/Te feed ratio leads to smaller size and higher PL QY; under 4:1 Ag/Te feed molar ratio, addition of secondary phosphine leads to narrower size distribution and excellent colloidal stability; under 6:1 Ag/Te feed molar ratio, excess 1-dodecanethiol as a strong ligand slows the nucleation and results in fewer nuclei, leading to a broad size distribution and poor optical properties; additional n-trioctyl phosphine as a weak ligand provides better colloidal stability; and another weak ligand n-tributylphosphine improves Ag2Te QD colloidal stability, focuses size distribution, and enhances PL QY. After optimization relatively large Ag2Te QDs with distinct excitonic absorption peaks (~1050 – 1450 nm) and PL emission peak 1.3 – 1.7 µm (QY up to 6.2%) were obtained. NIR-II photodetection has been demonstrated with a responsivity of ~1.5 mA/W at 1400 nm.2 More recently, we have been developing Sn-based chalcogenide QDs and obtained preliminary photodetection results. These results demonstrate that Ag and Sn chalcogenide QDs offer a low-toxicity route for low-cost fabrication of NIR-II photodetection. Reference: [1] Graddage N, Ouyang J, Lu J, Chu TY, Zhang Y, Li Z, Wu X, Malenfant PRL, Tao Y. Near-Infrared-II Photodetectors Based on Silver Selenide Quantum Dots on Mesoporous TiO2 Scaffolds. ACS Applied Nano Materials 2020, 3: 12209–12217.[2] Ouyang J, Graddage N, Lu J, Zhong Y, Chu TY, Zhang Y, Wu X, Kodra O, Li Z, Tao Y, Ding J. Ag2Te Colloidal Quantum Dots for Near-Infrared-II Photodetectors. ACS Applied Nano Materials 2021, 4: 13587–13601. Keywords: Environmentally Friendly; Near Infrared; Quantum Dots; Photodetection.

Multi-modal flexible and inexpensive plasmonic metasurface for wide range of refractive index sensing

Abstract A plasmonic metasurface containing nanobumps of sub-wavelength feature size arranged in a hexagonal pattern on a flexible substrate and covered with a thin film of gold is investigated as a refractive index sensor. The chosen polymer patterns coated with gold aid in activating the surface plasmon polariton modes. Using numerical calculations, it is shown that this surface can exhibit plasmonic effect with an extremely shallow pattern height of 92.5 nm and minimal thickness of 25 nm of gold over it. The excitation of the plasmonic modes is confirmed using electric field profiles calculated at the relevant wavelengths. As the surface is highly sensitive to changes in the cladding index, and the chosen design aids in exciting three plasmon modes that are suitably well-separated in wavelength, this surface can be used for an extremely wide range of refractive index sensing because each mode contributes uniquely to a different range of refractive index. The results establish that the metasurface is suitable for a variety of applications, including gas detection with a sensitivity of 633 nm/RIU using mode-1, identifying SARS-CoV-2 viral molecules with a sensitivity of 428 nm/RIU using mode-2 and 238 nm/RIU using mode-3, and discriminating between normal and diseased brain tissues in the cerebrospinal fluid in the high-index range using mode-3. The prototype metasurface is made using a cost-effective soft lithography technique using an economical master mould. The inexpensive technique of fabrication, use of very thin metal film, and wavelength of detection lying within the visible to near infrared range imply a low-cost sensor. The structural and optical characterization of the prototype validates the numerical study of the sample.

Spectrophotometric-Based Sensor for the Detection of Multiple Fertilizer Solutions

The online detection of fertilizer solution information is a crucial link in the implementation of intelligent and precise variable fertilization techniques. However, achieving simultaneous rapid online detection of multiple fertilizer components is still challenging. Therefore, a rapid detection method based on spectrophotometry for qualitative and quantitative identification of four fertilizers (typical N, P, and K fertilizers: KNO3, (NH4)2SO4, KH2PO4, and K2SO4) was proposed in this work. Full-scan absorption spectra of fertilizer solutions at varying concentrations were obtained using a UV–visible/near-infrared spectrophotometer. By assessing the linear fit between fertilizer concentration and absorbance at each wavelength within the characteristic band, the characteristic wavelengths for KNO3, (NH4)2SO4, KH2PO4, and K2SO4 were identified as 214 nm, 410 nm, 712 nm, and 1708 nm, respectively. The identification method of fertilizer type and the prediction model of concentration were constructed based on characteristic wavelength and the Lambert–Beer law. Based on the above analysis, a four-channel photoelectric sensor was designed with four LEDs emitting wavelengths closely matched to characteristic wavelengths for fertilizer detection. A detection strategy of “qualitative analysis followed by quantitative detection” was proposed to realize the online detection of four fertilizer types and their concentrations. Evaluation of the sensor’s performance showed its high stability, with an accuracy of 81.5% in recognizing fertilizer types. Furthermore, the relative error of the sensor detection was substantially less than ±15% for the fertilizer concentrations not exceeding 80 mg/L. These results confirm the capability of the sensor to meet the practical requirements for online detection of four fertilizer types and concentrations in the field of agricultural engineering.