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As a prescription drug, retinoic acid is listed as a banned cosmetic additive in the EU and China regulations. Currently, spectrophotometric methods, including thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), and HPLC–MS/MS, are commonly used for the determination of retinoic acid. As these conventional methods require complex pretreatment and are time-consuming, chemical derivatization combined with paper spray ionization mass spectrometry was developed for the fast detection of retinoic acid in cosmetics. N,N-dimethylpiperazine iodide (DMPI) was utilized as a derivatization reagent. Carboxylic acid in retinoic acid was derivatized to carry a positive charge and was subjected to mass spectrometry analysis. Results showed that compared with non-derivatized compounds, the detection limit was increased by about 50 times. The linearity in the range of 0.005–1 μg·mL−1 was good. The limit of detection (LOD) was 0.0013 μg·mL−1, and the limit of quantification (LOQ) was 0.0043 μg·mL−1. The recoveries of spiked samples were in the range of 95–105%, and the RSDs were below 5%. Derivatization and paper spray ionization MS render a quick, sensitive, and accurate method for the detection of retinoic acid in a complex matrix. [ABSTRACT FROM AUTHOR]

Rationale: Plasma‐based ionization sources play a vital role in rapidly analyzing diverse compounds without extensive sample pretreatment. In contrast to other sources, DC voltage‐based ionizations are more advantageous due to their high analytical sensitivity and good tandem with commercially available mass spectrometers without extra power supplies. However, their performance is at the risk of high current DC voltage and helium flow rate, which poses significant challenges to practical operation and increased expense. Methods: In this work, we propose a novel focusing plasma desorption ionization (FPDI) in which a visible plasma beam is favorably generated between a conducting wire in a polymeric tube and a counter electrode composed of metal mesh and filter paper drilled with holes. A systematic investigation has been conducted on the influences of the geometry of drilled holes in filter paper, applied DC voltage, helium flow rate, and filter paper size. The optimized system is used to analyze various pesticides in fluid foodstuffs. Results: Compared to metal mesh and conducting paper as the counter electrode for FPDI‐MS, combining metal mesh and filter paper drilled holes improved the analysis sensitivity by a factor of more than five. By applying the developed protocol for determining pesticides in complex matrixes such as orange juice and milk, a limit of detection as low as 1.3–3.0 ng mL−1 could be achieved. Conclusions: A novel FPDI‐MS technique has been developed by combining metal mesh and filter paper drilled with holes as the counter electrode and sample carrier. The corresponding improvement in analysis sensitivity facilitates the future expansion of FPDI‐MS applications into different pesticides and other compounds in complex matrixes. [ABSTRACT FROM AUTHOR]

In recent years, paper-based Surface-enhanced Raman spectroscopy (SERS) substrates have received extensive attention in the field of rapid analysis. However, obtaining quantitative SERS results is still challenging because of the inferior uniformity originating from the irregular morphology of the filter paper. In this work, a novel paper-fluidic SERS sensor was developed and its in-depth applications in the real-word quantitative analysis of contaminants in complex matrices were demonstrated. In particular, the Au@Ag core-shell nanospheres were labeled with an internal standard molecule to successfully normalize the fluctuation of the SERS signal caused by the microstructure of the filter paper, which could significantly improve the detection accuracy and accomplish the SERS quantitative analysis. In addition, a facile and robust strategy for the fabrication of a paper-based SERS sensor, which uses a dropper and mask to transfer the nanoparticle monolayers, was developed. This convenient and flexible approach effectively achieved a precise patterned assembly of nanoparticles on the filter paper. Furthermore, the paper-fluidic SERS sensor was fabricated by cutting and packaging for two detection modes, i.e., lateral-flow and vertical-flow, which generates the functionalization of the paper-based SERS substrate. Both detection modes integrated sample pretreatment and sample enrichment with SERS detection were applied to accurately detect the pesticide thiram in a complex sample of orange juice with pulp. In summary, this paper-fluidic SERS sensor with a simple preparation process and integrated functions is an ideal candidate for real sample analysis without pretreatment. Image 1 • Internal standard method was used to improve the uniformity of paper-based sensor and complete SERS quantitative analysis. • A facile strategy was developed with aid of dropper and mask to achieve precise assembly of nanoparticles on filter paper. • Lateral-flow and vertical-flow detection modes were applied to accurately measure the pesticide in orange juice with pulp. [ABSTRACT FROM AUTHOR]

Rationale: The burgeoning concern of N‐nitrosamine (NAM) contamination found in various pharmaceutical compositions has increased the demand for rapid and reliable screening methods to better assess the breadth of the problem. These carcinogenic compounds are also found in food, water, and soil, and they have been used in poison‐related homicides. Methods: A combination of complementary, ambient ionization methods, paper spray ionization (PSI) and filter cone spray ionization (FCSI)‐mass spectrometry (MS), was characterized towards trace‐level residue screening of select NAMs (e.g., N‐nitrosodimethylamine, N‐nitrosodiethylamine, N‐nitrosodibutylamine) directly from complex and problematic matrices of interest, including prescription and over‐the‐counter tablets, drinking water, soil, and consumable goods. Spectral data for analyte confirmation and detection limit studies were collected using a Thermo LCQ Fleet ion trap mass spectrometer. Results: PSI‐MS and FCSI‐MS readily produced mass spectral data marked by their simplicity (e.g., predominantly protonated molecular ions observed) and congruence with traditional electrospray ionization mass spectra in under 2 min. per sample. Both methods proved robust to the complex matrices tested, yielding ion signatures for target NAMs, as well as active pharmaceutical ingredients for analyzed tablets, flavorants inherent to food products, etc. Low part‐per‐million detection limits were observed but were shown dependent on sample composition. Conclusions: PSI‐MS and FCSI‐MS were successful in detecting trace‐level NAMS in complex liquid‐ and solid‐phase matrices with little to no prior preparation. This work suggests that these methodologies can provide a means for assessing problematic pharmaceutical adulterants/degradants for expedited quality control, as well as enhancing environmental stewardship efforts and forensic investigations. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman spectroscopy (SERS) is an emerging analytical technique for chemical analysis, which is favourable due to its combination of short measurement time, high sensitivity and molecular specificity. However, the application of SERS is still limited, largely because in real samples the analyte is often present in a complex matrix that contains micro/macro particles that block the probe laser, as well as molecular contaminants that compete for the enhancing surface. Here, we show a simple and scalable spray-deposition technique to fabricate SERS-active paper substrates which combine sample filtration and enhancement in a single material. Unlike previous spray-deposition methods, in which simple colloidal nanoparticles were sprayed onto solid surfaces, here the colloidal nanoparticles are mixed with hydroxyethyl cellulose (HEC) polymer before application. This leads to significantly improved uniformity in the distribution of enhancing particles as the film dries on the substrate surface. Importantly, the polymer matrix also protects the enhancing particles from air-oxidation during storage but releases them to provide SERS enhancement when the film is rehydrated. These SERS-paper substrates are highly active and a model analyte, crystal violet, was detected down to 4 ng in 10 μL of sample with less than 20% point-by-point signal deviation. The filter paper and HEC effectively filter out both interfering micro/macro particles and molecular (protein) contaminants, allowing the SERS-paper substrates to be used for SERS detection of thiram in mud and melamine in the presence of protein down to nanogram levels without sample pre-treatment or purification. [ABSTRACT FROM AUTHOR]

Paper-based analytical devices (PADs) are highly effective tools due to their low cost, portability, low reagent accumulation, and ease of use. Molecularly imprinted polymers (MIP) are also extensively used as biomimetic receptors and specific adsorption materials for capturing target analytes in various complex matrices due to their excellent recognition ability and structural stability. The integration of MIP and PADs (MIP-PADs) realizes the rapid, convenient, and low-cost application of molecular-imprinting analysis technology. This review introduces the characteristics of MIP-PAD technology and discusses its application in the fields of on-site environmental analysis, food-safety monitoring, point-of-care detection, biomarker detection, and exposure assessment. The problems and future development of MIP-PAD technology in practical application are also prospected. [ABSTRACT FROM AUTHOR]

Fluoroquinolones (FQs) are widely used for their excellent antimicrobial properties, yet their release into aquatic environments pose risks to ecosystems and public health. The accurate monitoring and analysis of FQs present challenges due to their low concentrations and the complex matrices found in actual environmental samples. To address the need for auto-pretreatment and on-line instrumental analysis, developing new microextraction materials and protocols is crucial. Such advancements will provide better analytical assurance for the effective extraction and determination of FQs at trace levels, which is of great significance to environmental protection and human health. In this work, we presented a Co2+ mediated paper-based molecularly imprinted polymer chip (CMC@Co-MIP), combined with UPLC analysis, to develop an effective analytical method for identifying and quantifying trace amounts of ciprofloxacin (CIP) and enrofloxacin (ENR) in water samples. Notably, the addition of Co2+ in CMC@Co-MIP helped to capture the template molecule CIP through coordination before imprinting, which significantly improved the ordering of the imprinted cavities. CMC@Co-MIP exhibited a maximum adsorption capacity up to 500.20 mg g−1 with an imprinting factor of 4.12, surpassing previous reports by a significant margin. Furthermore, the enrichment mechanism was extensively analyzed by various characterization techniques. The developed method showed excellent repeatability and reproducibility (RSD < 13.0 %) with detection limits ranging from 0.15 to 0.21 μg L−1 and recoveries ranging from 64.9 % to 102.3 % in real spiked water samples. We developed a novel microextraction paper-based chip based on Co2+ mediation, which effectively improved the selectivity and convenience of extracting FQs. This breakthrough allowed the chip to have a high enrichment efficiency as well as provide a robust on-line instrumental program. It also confirms that the imprinting scheme based on metal ion coordination is a high-performance strategy. [Display omitted] • A novel paper-based molecularly imprinted polymer chip (CMC@Co-MIP) was synthesized. • The imprinting protocol based on metal coordination was a high-performance strategy. • The chip showed excellent adsorption of fluoroquinolones, reaching 500.20 mg g−1. • The chip exhibited potentiality for environmental water samples pretreatment. [ABSTRACT FROM AUTHOR]

Adenosine triphosphate (ATP) determination has been used for many decades to assess microbial contamination for hygiene monitoring in different locations and workplace environments. Highly sophisticated methods have been reported, yet commercially available kits rely on a luciferase–luciferin system and require storage and shipping at controlled temperatures (+4 or −20 °C). The applicability of these systems is limited by the need for a secure cold chain, which is not always applicable, especially in remote areas or low-resource settings. In this scenario, easy-to-handle and portable sensors would be highly valuable. Prompted by this need, we developed a bioluminescence paper biosensor for ATP monitoring in which a new luciferase mutant was combined with a metal–organic framework (MOF); i.e., zeolitic imidazolate framework-8 (ZIF-8). A paper biosensor was developed, ZIF-8@Luc paper sensor, and interfaced with different portable light detectors, including a silicon photomultiplier (SiPM) and smartphones. The use of ZIF-8 not only provided a five-fold increase in the bioluminescence signal, but also significantly improved the stability of the sensor, both at +4 and +28 °C. The ATP content in complex biological matrices was analyzed with the ZIF-8@Luc paper sensor, enabling detection down to 7 × 10−12 moles of ATP and 8 × 10−13 moles in bacterial lysates and urine samples, respectively. The ZIF-8@Luc sensor could, therefore, be applied in many fields in which ATP monitoring is required such as the control of microbial contamination. [ABSTRACT FROM AUTHOR]

This article introduces a novel approach by coupling paper points with hollow fiber membrane for electroextraction (PP–HF-EE). The method was innovatively applied to extract methylene blue (MB) from large water volumes (up to 580 mL). A comprehensive study of six key parameters – organic filter, acceptor and donor phase composition, extraction time, applied voltage, and sample volume – was conducted using conventional flatbed scanning and digital image analysis. Our results revealed that extraction performance was primarily influenced by time, with low voltages (50 V) and low-conductivity organic filters (1-decanol) yielding comparable results to higher settings (300 V or 1-pentanol). Under optimized conditions (50 V, 60 min, 1-decanol as the organic filter), analytical performance parameters were assessed, demonstrating acceptable precision (RSD <18% for intra- and inter-day measurements) within a linear range of 5–100 μg L−1 (r = 0.98). PP–HF–EE demonstrated reliability through stable and reproducible electric current measurements during all extraction studies. Utilizing an extremely cost-effective detection system, PP–HF–EE achieved detection limits in the low ppb range, highlighting its potential as a promising variation of electromembrane extraction for environmental sample analysis. [Display omitted] • A new electroextraction approach for environmental samples was presented. • Paper point after extraction was subsequently examined by digital image analysis. • Quantification of methylene blue in tap water was achieved in the low ppb range. • The new electroextraction approach might be promising for environmental analysis. [ABSTRACT FROM AUTHOR]

Presently, the use of several pesticides has been continuously rising owing to the increase in the production of food materials to meet the requirements of the growing population of the world. The safety of food materials with regards to pesticides is an important health concern for people. With this aim, we have developed a smartphone-assisted paper-based sensor impregnated with citrate capped Cu@Ag core–shell nanoparticles (NPs) for selective determination of phenthoate pesticides in water and food samples. The mechanism for selective detection is based on the high affinity of phenthoate to interact with silver NPs present on the surface of CuNPs, which results in aggregation and a change in the color of the paper device. Furthermore, the proposed mechanism and interaction of phenthoate with Cu@Ag NPs was theoretically investigated by density functional theory (DFT) using Gaussian 16.0 software. The linear range for the determination of phenthoate was found in the range of 50–1500 μg L−1, with a limit of detection of 15 μg L−1, and a 92.6 to 97.4% recovery, and the interference studies demonstrated the selectivity for the determination of the target analyte from complex sample matrices. Finally, paper impregnated with Cu@Ag was exploited for the monitoring of the phenthoate pesticide in different water and food samples. The advantages of this paper-based sensor, coupled with a smartphone readout system, are that is it is user-friendly, easy-to-use, cost-effective, and can be applied at the sample source compared to sophisticated analytical instruments. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fabrication of α-glucosidase immobilized paper-based bioreactor. • High catalytic activity for immobilized α-glucosidase with C-terminus external. • Simultaneous ligand screening and visual ratiometric evaluating inhibitory activity. • Successful applications for Duzhong leaves and navel orange peels. • Molecular docking verified interactions of screened compounds to α-glucosidase. It is integral to establish methods to investigate inhibitory activity and screen inhibitors to α-glucosidase (α-Glu) from complex natural products. Here, α-Glu immobilized paper-based bioreactor platform was firstly developed for simultaneous ligand screening and visual ratiometric evaluating inhibitory activity. N-terminus of α-Glu was anchored on paper with chitosan and glutaraldehyde as cross-linking reagents. Smaller Michaelis constant (K m) for immobilized α-Glu (10.64 mM) than free α-Glu (15.63 mM) indicated higher catalytic activity. Sample (5 μL) was dropped on α-Glu immobilized paper for incubation, potent inhibitors would complex with α-Glu, while unbound compounds could be washed off. By chromatographic analyzing eluents from α-Glu and inactive α-Glu immobilized paper, potent inhibitors could be screened out. Simultaneously, activity of immobilized α-Glu was evaluated by fabricating visual ratiometric fluorescent system using ascorbic acid, Cu2+, and o -phenylenediamine without the interference of complex matrix. The developed platform was validated by model mixtures (positive control acarbose, IC 50 0.88 mg/mL; and negative control gallic acid, negligible inhibition at 5 mg/mL), and applied for real crude extracts. α-Glu inhibitory activities were visually detected for Duzhong leaves and navel orange peels (43.6 % and 26.0 % inhibition at 10 mg/mL), and four flavonoids were screened, identified, and verified as α-Glu inhibitors. Further, molecular docking studies revealed the possible inhibitory mechanisms, which came from the significant affinity interaction by forming hydrogen bonds. Results suggested the convenience, specificity, reliability, and efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

• A ratiometric fluorescent strip is designed based on IFE for detecting Sudan I-IV. • The fluorescent spectrum of Tm@Er has more overlap with the absorption of Sudan I-IV. • Single Tm@Er with core–shell structure provides a more stable ratiometric signal. • UiO-66 improve the adsorption and DMIPs realize the selective detection of Sudan I-IV. • Sensitive and portable application is realized in chilli powder with complex matrix. The addition of Sudan dyes with carcinogenic effects to food threatens human health. Herein, a ratiometric fluorescence strip consisting of core–shell upconversion particles (NaYF 4 :Yb,Tm@NaYF 4 :Yb,Er), metal–organic frameworks and dual-template molecularly imprinted polymers was developed to selectively and sensitively detect four Sudan dyes based on inner filter effect (detection time only takes 8 min). The high adsorption capacity of metal–organic frameworks and the greater overlap between the emission of NaYF 4 :Yb,Tm@NaYF 4 :Yb,Er and the absorbance of four Sudan dyes enable the signal responses to be more sensitive. The limits of detection in chilli powder samples are as low as 29.87 ng/g, 37.55 ng/g, 47.89 ng/g and 51.02 ng/g, with satisfactory recovery (93.32–103.4%) and minor relative standard deviations (≤4.3%). This method broadens the idea for low-cost and portable detection of multiple illegal additives in complex substrates with high selectivity and sensitivity based on one kind of fluorescent strip. [ABSTRACT FROM AUTHOR]

• Unmodified paper is used for the isolation of biogenic amines from beer samples. • The analysis of the extracts by MS provides LODs as low as 0.06 mg L−1. • The simultaneous extraction of several samples and the short analysis time (2 min) increases the sample throughput. • Eight different beer samples have been analyzed by the standard addition method. While current trends in Green Analytical Chemistry aim at reducing or simplifying sample treatment, food usually comprises complex matrices where direct analysis is not possible in most cases. In this context, sample treatment plays a pivotal role. Biogenic amines are naturally formed in many foodstuffs due to the action of microorganisms, while their presence has been associated with adverse health effects. In this work, the extraction of seven biogenic amines (cadaverine, histamine, phenylethylamine, putrescine, spermidine, spermine, and tyramine) from beer samples has been simplified using laboratory filter paper as sorbent without any further modification. The analysis of the eluates by direct infusion mass spectrometry reduces the time of analysis, increasing the sample throughput. This simple but effective method enabled the determination of the analytes with limits of detection as low as 0.06 mg L−1 and relative standard deviations better than 11.9%. The suitability of the method has been assessed by analyzing eight different types of beers by the standard addition method. [ABSTRACT FROM AUTHOR]

Paper spray high-resolution accurate mass spectrometry is a fast and versatile analysis method. This ambient ionization technique enables the quantitation of xenobiotics in complex biological matrices without chromatography or conventional sample extraction. The simplicity, rapidity, and affordability of the paper spray mass spectrometry (PS-MS) method make the technique especially attractive for clinical investigations where fast and affordable sample analysis is crucial. A new PS-MS method for the quantitation of voriconazole in equine tears was developed and validated. For a concentration range of 10 to 1000 ng/mL, good linearity (R2 > 0.99), inter- and intra-run precision (coefficient of variation (CV) max. 11.9%), accuracy (bias of the nominal concentration ± 13.9%), and selectivity (signal areas of the double blanks represent 0.13 ± 0.05% of the lower limit of quantitation (LLOQ) signal in equine tears) were observed. The quantitation of voriconazole was based on three product ions and calculated relative to the isotope-labeled internal standard, voriconazole-d3, which had a final concentration of 250 ng/mL in the standards and samples. The matrix effect of the method showed an ionization suppression by reduction of the voriconazole response to 63.6%, 70.2%, and 81.9% for 30 ng/mL, 450 ng/mL, and 900 ng/mL in equine tears compared with voriconazole in solvent (methanol:water, 50:50, v:v). The method was used to analyze 126 study samples collected for a pharmacokinetic study investigating a novel approach for treatment of fungal keratitis in horses. Therefore, the integrity of the sample dilution (n = 6, CV 6.90%, and bias of nominal concentration + 8.40%) and the carryover effect (increase from 0.33 ± 0.21% to 1.33 ± 0.89% of the signal of the LLOQ) was further investigated. To our knowledge, this method is the first application of PS-MS for quantitation of drug concentrations in tears from any species. [ABSTRACT FROM AUTHOR]

Nickel is one of the most common allergens found in cosmetics: a high exposure to nickel can cause serious effects on human health, as contact dermatitis or eczema. Considering the spread of this type of allergy among the population and the predominant use of cosmetic products, use portable and easy-to-use devices, which allow a quick and accurate assessment of nickel above the permitted limits, could represent a valid and alternative tool for the protection of human health. In this study, we developed a hybrid paper-polyester printed strip for fast, simple, and low-cost determination of nickel at concentrations consistent with the allowable limits in cosmetics, exploiting the differential pulse adsorptive stripping voltammetry in the presence of dimethylglyoxime as Ni-complexing agent. We report a novel configuration to produce an integrated fully-printed electrochemical device, in which the screen-printed electrode, printed on polyester, is successfully combined with a wax-printed filter paper disk in order to allow the investigation in treatment of complex matrices such as cosmetics ones. In addition, the use of filter paper allows to store all the reagents necessary for carrying out the determination. The method developed has allowed to work with small amount of sample (microliters level), obtaining a detection limit equal to 2 µM in standard solution and 5 µM in the two chosen matrices, namely cream and a synthetic gel. In order to evaluate the applicability, the device was also tested for the analysis of two commercial products, obtaining satisfactory results in terms of sensitivity and repeatability. The accuracy has been also evaluated by inductively coupled plasma-mass spectrometry (ICP-MS) measurements, with high correlation between the two approaches. [Display omitted] [ABSTRACT FROM AUTHOR]

The electrochemical degradation of tetraethylrhodamine, commonly known as Rhodamine B (RhB) in acidic aqueous solutions, was examined utilizing a platinum grid anode and a stainless steel cathode. This dye is a substance used to impart color to cotton, silk paper, bamboo, weed, leather, and other materials as well as to prepare carbon paper, ball pen, stamp pad inks, paintings, etc. In case of being swallowed by humans and animals, this chemical compound causes an irritation to the skin, eyes, gastrointestinal and respiratory tract, in addition to phototoxic and photoallergic responses. Experimental evidence of carcinogenicity, reproductive and developmental toxicity, neurotoxicity, and chronic toxicity in people and animals has been established. The effects of various experimental parameters on the RhB dye degradation were investigated. The optimum conditions are: a current of 100 mA, Fe(II) = 10 mg/L, and Na2SO4 = 10 mg/L. All the experiments were carried out at pH = 2.5. The % removal = 98.75 after 120 min. The combination of electro-Fenton and ultrasonic irradiation with a low frequency (sono-electro-Fenton process) was also studied. Sonoelectrochemical treatment of RhB-contaminated water yielded a significant, considerable percentage of 99% after 90 min at a current of 100 mA. [ABSTRACT FROM AUTHOR]

In this article, we first report a simple fabrication technique to create Parafilm®-laminated microfluidic paper-based analytical devices (µPADs) with a high resolution and then introduce novel engineered detection zones (D-zones) to enhance color uniformity without any chemical modifications. The Parafilm®-heating-laser cutting fabrication method comprises of three steps: 1) flattening a Parafilm® layer on paper, 2) heating in an oven at 90 °C for 30 min, and 3) CO 2 laser ablation of the patterns. This method enabled laminated µPADs with a minimum barrier width of 172 ± 15 µm, with resistance to various organic solvents and surfactant solutions. Using this technique, µPADs with two types of engineered D-zones were fabricated. The multi-inlet D-zone had four micro-inlets (<500 µm width), enabling sample entrance into the D-zone from four directions simultaneously towards the center. The segmented D-zone had four segments each with its own micro-inlet allowing for separate reactions to occur in miniaturized segments simultaneously. Using an enzymatic glucose assay for the colorimetric reaction, the multi-inlet and segmented D-zones significantly decreased color gradient from 28.77 ± 1.49 to 12.35 ± 1.18 and 8.95 ± 0.98 %, respectively, compared to the conventional devices. We further used the µPADs with segmented D-zones for the detection of glucose in artificial urine in the clinically relevant range of 2–50 mM, where R2 > 0.99 of the fitted curve showed an excellent correlation between the generated signals and the glucose concentrations. Also, compared to the conventional devices, the engineered D-zones showed improved precision and reproducibility and a better linear range. Finally, spiked real human urine samples were tested, demonstrating the applicability of the engineered devices for real-world applications. Overall, with a simple fabrication method and a novel design for color uniformity, this paper contributes to the advancement of µPADs and paves the way towards commercialization. [Display omitted] • A simple method to fabricate Parafilm®-laminated µPADs is explained. • Small computer-designed channels can be created with resistance against different chemicals. • Two engineered detection zones are introduced: multi-inlet and segmented. • The novel detection zones enhanced color uniformity of glucose assay significantly. • The devices were able to detect glucose in complex matrices, i.e., real urine samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • Acidification of paper substrates eliminate super-Nernstian response of Pb2+-ISEs. • 3D approximate (concentration-EMF-pH) analyses of the Pb2+-ISEs was introduced. • Pb2+-ISEs acceptable operational pH range of paper substrate with solution was 3–4. • Colour-coded graph was proposed to match paper substrates with unbuffered samples. • Pb2+ analysis in complex environmental samples was successfully performed. To address analysis of heavy metals in samples containing low volumes and/or high solid-to-liquid contents, microfluidic paper-based solution sampling coupled with Pb2+-ISEs was investigated. The acidification of paper substrates prior to their use was found effective at eliminating the otherwise observed super-Nernstian response of Pb2+-ISEs. Acidified paper substrates (at different pH) were evaluated and through 3D approximate (concentration-EMF-pH) analyses of the Pb2+-ISEs responses coupled with acidified paper substrates, the acceptable operational pH range (for paper substrate containing sample solution) of the potentiometric sensors was found to be between 3–4. Furthermore, to simplify the analytical protocol of heavy metal sensing using Pb2+-ISEs coupled with microfluidic paper-based solution sampling, a colour-coded matching graph was proposed to match the appropriate acidified paper substrate to the pH of the unbuffered sample solution. Such an approach was used for determination of Pb2+ in various complex environmental samples with small volumes of solution and/or high solid-to-liquid ratios, such as wet soil, street runoff, chemical spillage and plant dew. Although the samples were characterized with high ionic complexity, determinations by potentiometry and ICP-OES were found to be comparable, which validates the use of acidified paper substrates in reliable determination of lead(II) in complex sample matrices. [ABSTRACT FROM AUTHOR]

The detection of glycans and glycoconjugates has gained increasing attention in biological fields. Traditional mass spectrometry (MS)-based methods for glycoconjugate analysis are challenged with poor sensitivity when dealing with complex biological samples. We developed a desalting paper spray mass spectrometry (DPS-MS) strategy to overcome the issue of signal suppression of carbohydrates in salted buffers. Glycans and glycoconjugates (i.e., glycopeptides, nucleotide sugars, etc.) in non-volatile buffer (e.g., Tris buffer) can be loaded on the paper substrate from which buffers can be removed by washing with ACN/H 2 O (90/10 v/v) solvent. Glycans or glycoconjugates can then be eluted and spray ionized by adding ACN/H 2 O/formic acid (FA) (10/90/1 v/v/v) solvent and applying a high voltage (HV) to the paper substrate. Our results showed that DPS-MS is applicable for direct detection of intact glycopeptides and nucleotide sugars as well as determination of glycosylation profiling of antibody, such as NIST monoclonal antibody IgG (NISTmAb). NISTmAb was deglycosylated with PNGase F to release N-linked oligosaccharides. Twenty-six N-linked oligosaccharides were detected by DPS-MS within a 5-min timeframe without the need for enrichment or derivatization. This work demonstrates that DPS-MS allows fast and sensitive detection of glycans/oligosaccharides and glycosylated species in complex matrices and has great potential in bioanalysis. [Display omitted] • DPS-MS can be used for directly analyzing glycans and glycoconjugates in non-volatile buffers. • DPS-MS can be used for directly identifying 26 glycans from PNGase F-digested antibody IgG. • DPS-MS is fast (less than 5 min each sample) and sensitive. [ABSTRACT FROM AUTHOR]

Sample loading, Element enrichment and Visualization processes. [Display omitted] • Novel designed lateral flow strip based on functional Pb (II) MIPs paper chip was successfully fabricated. • A newly designed μ PAD platform and visualization methodology was proposed. • The presented platform demonstrated sensitivity, rapidness and application ruggedness for real sample with 1.375 mg kg−1 (LOD) and 2.5–100 mg kg−1 (linear range) A high-performance lateral flow and paper-based microfluidic device (μ PAD) was constructed to develop a rapid read-out analytical platform for heavy metal elements (Pb (II)) in green tea with complex matrices. The entire analytical device was integrated with several functional parts, including a liquid flow channel and an enrichment visualization zone prepared by the molecularly imprinted polymer (MIP) protocol. Under the optimal conditions, the Pb (II) content in tea products can be sensitively and specifically analyzed using an in situ visualization readout. Herein, a rapid visual read-out analysis of the lead level can be achieved by overcoming the other co-existing interfering elements in the traditional green tea sample. The ionic imprinted paper chip can effectively capture the Pb (II) of the digested sample solution, and a visualization sensing process occurred between the metal elements and a chelating visual reagent with high sensitivity and selectivity in situ. Owing to the stable visualization performance, the constructed chip demonstrated good contrast, with a low background and easily recognizable colored spots. The linear range was 2.5–100 mg kg−1, and the limit of detection for Pb (II) in traditional green tea was 1.375 mg kg−1. In addition, other co-existing metal elements did not interfere with the analysis because of the appropriate pretreatment and selectivity of the paper-based chip. Furthermore, the analytical results for tea samples were verified by atomic absorption spectrophotometer (AAS) tests, which demonstrated the robustness and reliability of the proposed method. Therefore, the high-performance visualization lateral flow- μ PAD is a promising platform for the rapid analysis of metal element levels in food products. [ABSTRACT FROM AUTHOR]

There are increasing demands for fast and simple detection of pathogens in foodstuffs. Fluorescence analysis has demonstrated significant advantages for easy operation and high sensitivity, although it is usually hindered by a complex matrix, low bacterial abundance, and long-term bacterial enrichment. Effective enrichment procedures are required to meet the requirements for food detection. Here, boronate-functionalized cellulose filter paper and specific fluorescent probes were combined. An integrated approach for the enrichment of detection of Staphylococcus aureus was proposed. The modification of polyethyleneimine demonstrated a significant effect in enhancing the bacterial enrichment, and the boronate affinity efficiency of the paper was increased by about 51~132%. With optimized conditions, the adsorption efficiency for S. aureus was evaluated as 1.87 × 108 CFU/cm2, the linear range of the fluorescent analysis was 104 CFU/mL~108 CFU/mL (R2 = 0.9835), and the lowest limit of detection (LOD) was calculated as 2.24 × 102 CFU/mL. Such efficiency was validated with milk and yogurt samples. These results indicated that the material had a high enrichment capacity, simple operation, and high substrate tolerance, which had the promising potential to be the established method for the fast detection of food pathogens. [ABSTRACT FROM AUTHOR]

Here, we developed a microfluidic paper device by combining ion-selective electrodes (ISE) and a distance-based paper device (dPAD) for simultaneous potentiometric and colorimetric detection of urine electrolytes including K+, Na+ and Cl−. The working and reference electrode zones were coated with polystyrene as a non-ionic polymer to improve hydrophobic properties on the paper surface for fabrication of K+-ISE and Na+-ISE. The layer of polymer coating was optimized to enhance the sensitivity of the ISEs. Under optimized conditions, the electrode surfaces were modified with carbon black to improve the electrochemical characteristics of the ISEs. The ISEs showed good performance with sensitivities of 54.14 ± 3.94 mV per decade and 55.08 ± 1.15 mV per decade for K+ and Na+ within the linear concentration range 0.100 mM–100 mM K+ and 5 mM–1 M Na+, respectively. The limits of detection (LOD) were 0.05 mM and 1.36 mM for K+ and Na+, respectively. The linear working range of Cl− was 0.50 to 50 mM and the LOD and limit of quantification (LOQ) were found to be 0.16 ± 0.05 mM (3SD) and 0.53 ± 0.05 mM (10SD), respectively. The dual-mode ISE-dPAD was validated in human urine and recoveries were obtained as 90–108%, 94–105%, and 90–96% for K+, Na+, and Cl−, respectively, showing successful application of the developed device in a complex matrix. The ISE-dPAD has advantages including low-cost ($ 0.33 per test), eco-friendly, portability, simple operation, the need of low sample volume (100 μL), and simultaneous analysis on a single device. [ABSTRACT FROM AUTHOR]

The popularization of paper-based analytical devices (PADs) in analytical science has fostered research on enhancing their analytical performance for accurate and sensitive assays. With their superb recognition capability and structural stability, molecularly imprinted polymers (MIPs) have been extensively employed as biomimetic receptors for capturing target analytes in various complex matrices. The integration of MIPs as recognition elements with PADs (MIP-PADs) has opened new opportunities for advanced analytical devices with elevated selectivity and sensitivity, as well as a shorter assay time and a lower cost. This review covers recent advances in MIP-PAD fabrication and engineering based on multifarious signal transduction systems such as colorimetry, fluorescence, electrochemistry, photoelectrochemistry, and chemiluminescence. The application of MIP-PADs in the fields of biomedical diagnostics, environmental analysis, and food safety monitoring is also reviewed. Further, the advantages, challenges, and perspectives of MIP-PADs are discussed. Image 1 • Recent advances on the biomimetic paper-based analytical devices. • Construction strategies of MIP-PADs based on different signal readout modes. • Enhanced analytical performance of MIP-PADs in chemo/bioanalysis. [ABSTRACT FROM AUTHOR]

To increase milk production, antibiotics are administered to animals to provide weight gain and to prevent or treat diseases. The inappropriate use of these substances can lead to antibiotic resistance and allergic reactions and toxic effects to milk consumers. We describe the development of a simple, fast, portable, and low-cost microfluidic paper-based analytical device (μPAD) to quantify sulfonamides in milk using the inhibition of the colorimetric reaction between carbonic anhydrase (CA) and 4-nitrophenyl acetate. The main advantages presented by the μPAD include reproducible batch production, simple application, and precise analysis without previous treatment. The µPAD displayed good linearity (R2 ≥ 0.986) in a wide range of sulfonamides in milk (2.5 to 40.0 µmol L−1), being selective for the drugs even in a highly complex matrix. We expect that this device allows in situ monitoring of milk quality, reducing the prejudicial conditions associated with high concentrations of sulfonamides in milk. [ABSTRACT FROM AUTHOR]

• Thiomalic acid modified CDTE was utilized for visual detection of Ag+. • High sensitivity and selectivity for Ag+were achieved. • The detection limit of fluorescence spectrometry method for Ag+ was 13.16 nmol/L. • Paper-based sensors for Ag+ was carried out in a rapid, simple and effective way. • PLSR accurately quantified concentrations of Ag+ in matrices based on paper images. A fluorescence paper-based sensor method by simply using thiomalic acid modified CdTe (TMA-capped CdTe) was proposed for visual detection of silver ions (Ag+). Red-emission TMA-capped CdTe with a large amount of carboxyl groups on the surface could be combined with Ag+ by electrostatic interaction, thus leading to the fluorescence quenching. It was found that the adding of amino acids contributed to fluorescence recovery by the leaving of Ag+ on the surface of TMA-capped CdTe. Moreover, the more amino group, benzene and thiol group equipped in the structure of amino acid, the stronger fluorescence restoring of CdTe could be achieved. This fluorescence spectrometry method for Ag+ showed low detection of limit with the value of 13.16 nmol/L, with no response to other heavy metals, which demonstrating its high sensitivity and high selectivity for Ag+. More importantly, this paper-based sensor method combined with chemometrics could accurately identify and quantify different concentrations of Ag+ in different complex matrices. This fast, economical, accurate and effective approach exhibited a new idea for the on-site detection of Ag+, and was expected to be extended to the on-site detection of Ag+ in biological and environmental fields. [ABSTRACT FROM AUTHOR]

An improved step-by-step colorimetric method for determination of halides has been developed. The method is based on successive selective oxidation of iodide, bromide and chloride into corresponding free halogens, their extraction by airflow and colorimetric detection with different paper test-strips. This procedure can be performed in a single analyzed solution and possesses high selectivity and good sensitivity due to the extraction step. Three types of paper test-strips were examined: paper modified with tetramethylammonium iodide and starch, paper modified with methyl orange and paper modified with silver triangular nanoplates. Limits of detection for iodide, bromide and chloride are 0.01, 0.02, and 0.04 mg L−1 respectively in case of the last mentioned paper. The method was applied to the analysis of samples having complex matrices, such as various seafood, preserves, bread, and natural waters, showing good accuracy of the analysis with recoveries of 95–105% and relative standard deviations not higher than 6%. Image 1 • An improved step-by-step colorimetric method for determination of halides has been developed. • The method combines high selectivity and high sensitivity in complex matrices. • Colorimetric paper test-strips modified with silver triangular nanoplates were used. • The method can be implemented for various samples having complex matrices. • Only a minimal sample pretreatment is required. [ABSTRACT FROM AUTHOR]

In this study, a rapid clean-up approach to the microextraction of aquatic food samples based on disposable thin-layer chromatography (dTLC) was developed. First, slides with uniform brushed Gelatin 60 as the stationary phase on paper coated with polyvinyl chloride (PVC) were designed and fabricated successfully. Diethylstilbestrol (DES, mixture of cis- and trans-isomers), which was selected as a typical trace residue of an illegal additive in aquatic products, can be perfectly separated on the paper-based slide by designed solvent development. Under the optimum conditions, the trace amounts of DES in aquatic products can be detected by gas chromatography coupled with mass spectrometer (GC–MS) without obvious interferences from sample matrix. The analytical linearity of DES ranged from 1.0 μg kg−1 to 0.20 mg kg−1, with a detection limit of 0.20 μg kg−1. The present work demonstrated the reliability and applicability of dTLC slides as a preconcentration and clean-up method for the analysis of trace contaminants in food stuff with complex matrix. • A novel clean-up strategy based on paper-based thin layer chromatography • Successful application of paper-base TLC slides as sample pretreatment materials • Sensitive analysis of trace diethylstilbestrol (DES) residues in aquatic products • This method shows easy operation, cost-saved, rapid and environment friendly. [ABSTRACT FROM AUTHOR]

Electrochemical detection methods hold many advantages over their optical counterparts, such as operation in complex sample matrices, low-cost and high volume manufacture and possible equipment miniaturisation. Despite these advantages, the use of electrochemical detection is currently limited in the clinical setting. There is a wide range of potential electrode materials, selected for optimal signal-to-noise ratios and reproducibility when detecting target analytes. The use of carbon paste electrodes (CPEs) for electrochemical detection can be limited by their analytical performance, however they remain very attractive due to their low cost and biocompatibility. This paper presents the fabrication of an easy-to-make and use graphite powder/paraffin wax paste combined with a substrate produced via additive manufacturing and confirms its functionality for both direct and indirect electrochemical measurements. The produced CPEs enable the direct voltammetric detection of hexaammineruthenium(III) chloride and dopamine at an experimental limit of detection (ELoD) of 62.5 μM. The key inflammatory biomarker Interleukin-6 through an enzyme-linked immunosorbant assay (ELISA) was also quantified, yielding a clinically-relevant ELoD of 150 pg ml−1 in 10% human serum. The performance of low-cost and easy-to-use CPEs obtained in 0.5 hours is showcased in this study, demonstrating the platform's potential uses for point-of-need electroanalytical applications. [ABSTRACT FROM AUTHOR]

Mass spectrometry technology can realize dynamic detection of many complex matrix samples in a simple, rapid, compassionate, precise, and high-throughput manner and has become an indispensable tool in accurate diagnosis. The mass spectrometry data analysis is mainly to analyze all metabolites in the organism quantitatively and to find the relative relationship between metabolites and physiological and pathological changes. A feature construction of mass spectrometry data (MSFS) method is proposed to construct the features of the original mass spectrometry data, so as to reduce the noise in the mass spectrometry data, reduce the redundancy of the original data and improve the information content of the data. Chi-square test is used to select the optimal non-redundant feature subset from high-dimensional features. And the optimal feature subset is visually analyzed and corresponds to the original mass spectrum interval. Training in 10 kinds of supervised learning models, and evaluating the classification effect of the models through various evaluation indexes. Taking two public mass spectrometry datasets as examples, the feasibility of the method proposed in this paper is verified. In the coronary heart disease dataset, during the identification process of mixed batch samples, the classification accuracy on the test set reached 1.000; During the recognition process, the classification accuracy on the test set advanced to 0.979. On the colorectal liver metastases data set, the classification accuracy on the test set reached 1.000. This paper attempts to use a new raw mass spectrometry data preprocessing method to realize the alignment operation of the raw mass spectrometry data, which significantly improves the classification accuracy and provides another new idea for mass spectrometry data analysis. Compared with MetaboAnalyst software and existing experimental results, the method proposed in this paper has obtained better classification results. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to explore how hierarchical accountability can be enacted and accounting control systems mobilized in a way that promotes a sense of felt responsibility. Design/methodology/approach: The paper draws on interviews, shadowing and observations to explore the implementation of a strategy for "increasing accountability" in a Norwegian Oil Company. The case provided an opportunity to explore the dynamics of hierarchical accountability and felt responsibility, and in particular Roberts (2009) concept of "intelligent accountability", in an empirical context. Findings: The case study explores how the strategy of increasing accountability at OilCo was enacted around three operational issues; the control of costs, roles and relationships in the complex matrix structure, and the operation of the management system. It traces how the long history of Beyond Budgeting practices and philosophy in OilCo resulted both in an explicit recognition of the incompleteness of accounting numbers, and trust-based practices which avoided many of the dysfunctional individual and organizational effects typically associated with the exercise of hierarchical control. Originality/value: The paper explores empirically how OilCo's embrace of Beyond Budgeting practices and philosophy had created the conditions under which a more intelligent form of accountability could emerge. As a European case study, it calls into question the Anglo-American tradition of accounting research which suggests that externally imposed accountability within a hierarchy mitigates against employees' felt responsibility. [ABSTRACT FROM AUTHOR]

This paper deals with left star, star, and core partial orders for complex matrices. For each partial order, we present an order-isomorphism between the down-set of a fixed matrix B and a certain set (depending on the partial order) of orthogonal projectors whose matrix sizes can be considerably smaller than that of the matrix B. We study the lattice structure and we give properties of the down-sets. We prove that the down-set of B ordered by the core partial order and by the star partial order are sublattices of the down-set ordered by the left star partial order. We analize the existence of supremum and infimum of two given matrices and we give characterizations of these operations (whenever they exist). Some of the results given in the paper are already known in the literature but we present a different proof based on the previously established order-isomorphism. [ABSTRACT FROM AUTHOR]

This paper intends to show several inner product inequalities using the Cartesian decomposition of the operator. We utilize the obtained results to get norm and numerical radius inequalities. Our results extend and improve some earlier inequalities. Among other inequalities, it is revealed that if T is a n × n complex matrix with the imaginary part ℑT = T--T*/2i, then 1/2 max(∥TT* -- iℑT²∥1/2, ∥T*T + iℑT²∥1/2) ≤ ω(T) which is a significant improvement of the classical inequality 1/2 ℑTℑ ≤ ω(T). [ABSTRACT FROM AUTHOR]

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Additive manufacturing (AM) is a wide set of technologies that can be used for many different scopes. AM is now a well-integrated prototyping and development tool in most industrial endeavours, while proper end-product manufacturing has only seen very specific niche successes. Given the complexity of AM's matrix, which is full of discontinuities and non-trivial intercorrelations that play a relevant role in product design and development, it should not come as a surprise that not many end-product applications have succeeded in making use of it. This paper argues that understanding AM's complex matrix and correctly identifying suitable production niches for it are key elements of this issue, a topic for which existing literature and tools are scarce. The analysis of AM's status quo for end-product manufacturing and the review of existing approaches to integrate these technologies with product development are the basis used in this paper to propose a suitability assessment tool to fill this knowledge gap. [ABSTRACT FROM AUTHOR]

In this paper, we introduce the concept of reverse sharp ordering on Intuitionistic Fuzzy matrix (IFM) as a special case of minus ordering. We also introduce the concept of reverse left-T and right-T orderings for IFM as an analogue of left-star and right-star partial orderings for complex matrices. Several properties of these ordering are derived. We show that these ordering preserve its Moore-penrose inverse property. Finally, we show that these ordering are identical for certain class of IFM. [ABSTRACT FROM AUTHOR]

This paper provides additive perturbation bounds for the generalized core inverse $ A^{d,\dag } $ A d , † of a complex matrix A. Given perturbation matrix E, we first present upper bounds for $ \frac {\|(A+E)^{d,\dag }-A^{d,\dag }\|_{2}}{\|A^{d,\dag }\|_{2}} $ ‖ (A + E) d , † − A d , † ‖ 2 ‖ A d , † ‖ 2 under the condition $ \mathcal {R}(E)\subseteq \mathcal {R}(A^k), \mathcal {N}(A^{k}A^{\dag })\subseteq \mathcal {N}(E), {\rm where}\ k=\mathrm {ind}(A) $ R (E) ⊆ R (A k) , N (A k A †) ⊆ N (E) , where k = ind (A) , and then under the condition $ (A+E)(A+E)^{d,\dag }=AA^{d,\dag } $ (A + E) (A + E) d , † = A A d , † . We then explore an integral formula for the generalized core inverse of a perturbed matrix associated with a semi-stable matrix. Furthermore, a perturbation bound for $ \|(A+E)^{d,\dag }-A^{d,\dag }\|_{F} $ ‖ (A + E) d , † − A d , † ‖ F is obtained without conditions. Sufficient conditions for the continuity of the generalized core inverse can be obtained as a result. Finally, numerical examples are presented to illustrate the derived bounds. [ABSTRACT FROM AUTHOR]

For a germ of a variety V,0⊂CN,0$\mathcal {V}, 0 \subset \mathbb {C}^N, 0$, a singularity V0$\mathcal {V}_0$ of "type V$\mathcal {V}$" is given by a germ f0:Cn,0→CN,0$f_0: \mathbb {C}^n, 0 \rightarrow \mathbb {C}^N, 0$, which is transverse to V∖{0}$\mathcal {V}\setminus \lbrace 0\rbrace$ in an appropriate sense, such that V0=f0−1(V)$\mathcal {V}_0 = f_0^{-1}(\mathcal {V})$. In part I of this paper, we introduced for such singularities the Characteristic Cohomology for the Milnor fiber (for V$\mathcal {V}$ a hypersurface), and complement and link (for the general case). It captures the cohomology of V0$\mathcal {V}_0$ inherited from V$\mathcal {V}$ and is given by subalgebras of the cohomology for V0$\mathcal {V}_0$ for the Milnor fiber and complements, and is a subgroup for the cohomology of the link. We showed these cohomologies are functorial and invariant under diffeomorphism groups of equivalences KH$\mathcal {K}_{H}$ for Milnor fibers and KV$\mathcal {K}_{\mathcal {V}}$ for complements and links. We also gave geometric criteria for detecting the nonvanishing of the characteristic cohomology. In this paper, we apply these methods in the case V$\mathcal {V}$ denotes any of the varieties of singular m×m$m \times m$ complex matrices, which may be either general, symmetric, or skew‐symmetric (with m$m$ even). For these varieties, we have shown in another paper that their Milnor fibers and complements have compact "model submanifolds" for their homotopy types, which are classical symmetric spaces in the sense of Cartan. As a result, we first give the structure of the characteristic cohomology subalgebras for the Milnor fibers and complements as images of exterior algebras (or in one case a module on two generators over an exterior algebra). For links, the characteristic cohomology group is the image of a shifted upper truncated exterior algebra. In addition, we extend these results for the complement and link to the case of general m×p$m \times p$ complex matrices. Second, we then apply the geometric detection methods introduced in Part I to detect when specific characteristic cohomology classes for the Milnor fiber or complement are nonzero. We identify an exterior subalgebra on a specific set of generators and for the link that it contains an appropriate shifted upper truncated exterior subalgebra. The detection criterion involves a special type of "kite map germ of size ℓ$\ell$" based on a given flag of subspaces. The general criterion that detects such nonvanishing characteristic cohomology is then given in terms of the defining germ f0$f_0$ containing such a kite map germ of size ℓ$\ell$. Furthermore, we use a restricted form of kite spaces to give a cohomological relation between the cohomology of local links and the global link for the varieties of singular matrices. [ABSTRACT FROM AUTHOR]

This paper focuses on algorithms for the truncated Takagi factorization of complex symmetric matrices. The problem is formulated as a Riemannian optimization problem on a complex Stiefel manifold and then is converted into a real Riemannian optimization problem on the intersection of the real Stiefel manifold and the quasi-symplectic set. The steepest descent, the Riemannian nonmonotone conjugate gradient, Newton, and hybrid methods are used for solving the problem and they are compared in their performance for the optimization task. Numerical experiments are provided to illustrate the efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, we derive and analyze an algorithm for inverting quaternion matrices. The algorithm is an analogue of the Frobenius algorithm for the complex matrix inversion. On the theory side, we prove that our algorithm is more efficient than other existing methods. Moreover, our algorithm is optimal in the sense of the least number of complex inversions. On the practice side, our algorithm outperforms existing algorithms on randomly generated matrices. We argue that this algorithm can be used to improve the practical utility of recursive Strassen-type algorithms by providing the fastest possible base case for the recursive decomposition process when applied to quaternion matrices. [ABSTRACT FROM AUTHOR]

In this paper, we study dual quaternion, dual complex unit gain graphs, and their spectral properties in a unified frame of dual unit gain graphs. Unit dual quaternions represent rigid movements in the 3D space, and have wide applications in robotics and computer graphics. Dual complex numbers have found application in brain science recently. We establish the interlacing theorem for dual unit gain graphs, and show that the spectral radius of a dual unit gain graph is always not greater than the spectral radius of the underlying graph, and these two radii are equal if, and only if, the dual gain graph is balanced. By using dual cosine functions, we establish the closed form of the eigenvalues of adjacency and Laplacian matrices of dual complex and quaternion unit gain cycles. We then show the coefficient theorem holds for dual unit gain graphs. Similar results hold for the spectral radius of the Laplacian matrix of the dual unit gain graph too. [ABSTRACT FROM AUTHOR]

The Drazin inverse is connected with the notion of index and core-nilpotent decomposition whenever it is discussed in the context of ring of matrices over complex field. In the absence of Drazin inverse for a given element from an arbitrary associative ring (not necessarily with unity), in this paper, the notion of right (left) core-nilpotent decomposition has been introduced and established its relations with right (left) π -regular property. In fact, the class of such decomposition has been characterized. In case of regular ring, observed that an element is right (left) π -regular if and only if it has a right (left) core-nilpotent decomposition. In the process, several properties of sharp order in an associative ring are studied and with the help of the same, new characterizations of Drazin inverse over an associative ring are obtained and the relation between core-nilpotent decomposition and the Drazin inverse is obtained. [ABSTRACT FROM AUTHOR]

New characterizations for generalized inverses along the core parts of three matrix decompositions were investigated in this paper. Let A1, Â1 and Ã1 be the core parts of the core-nilpotent decomposition, the core-EP decomposition and EP-nilpotent decomposition of A ∈ Cn×n, respectively, where EP denotes the EP matrix. A number of characterizations and different representations of the Drazin inverse, the weak group inverse and the core-EP inverse were given by using the core parts A1, Â1 and Ã1. One can prove that, the Drazin inverse is the inverse along A1, the weak group inverse is the inverse along Â1 and the core-EP inverse is the inverse along Ã1. A unified theory presented in this paper covers the Drazin inverse, the weak group inverse and the core-EP inverse based on the core parts of the core-nilpotent decomposition, the core-EP decomposition and EP-nilpotent decomposition of A ∈ Cn×n, respectively. In addition, we proved that the Drazin inverse of A is the inverse of A along U and A1 for any U ∈ {A1, Â1, Ã1}; the weak group inverse of A is the inverse of A along U and Â1 for any U ∈ {A1, Â1, Ã1}; the core-EP inverse of A is the inverse of A along U and Ã1 for any U ∈ {A1, Â1, Ã1}. Let X1, X4 and X7 be the generalized inverses along A1, Â1 and Ã1, respectively. In the last section, some useful examples were given, which showed that the generalized inverses X1, X4 and X7 were different generalized inverses. For a certain singular complex matrix, the Drazin inverse coincides with the weak group inverse, which is different from the core-EP inverse. Moreover, we showed that the Drazin inverse, the weak group inverse and the core-EP inverse can be the same for a certain singular complex matrix. [ABSTRACT FROM AUTHOR]

A paper by the current authors Paul and Nelson [JASA Express Lett. 3(9), 094802 (2023)] showed how the singular value decomposition (SVD) of the matrix of real weights in a neural network could be used to prune the network during training. The paper presented here shows that a similar approach can be used to reduce the training time and increase the implementation efficiency of complex-valued neural networks. Such networks have potential advantages compared to their real-valued counterparts, especially when the complex representation of the data is important, which is the often case in acoustic signal processing. In comparing the performance of networks having both real and complex elements, it is demonstrated that there are some advantages to the use of complex networks in the cases considered. The paper includes a derivation of the backpropagation algorithm, in matrix form, for training a complex-valued multilayer perceptron with an arbitrary number of layers. The matrix-based analysis enables the application of the SVD to the complex weight matrices in the network. The SVD-based pruning technique is applied to the problem of the classification of transient acoustic signals. It is shown how training times can be reduced, and implementation efficiency increased, while ensuring that such signals can be classified with remarkable accuracy. [ABSTRACT FROM AUTHOR]

Soil mechanics traditionally have focused on studying pure clays and clean sands. However, natural soils and other geomaterials usually do not fall into these two classes. Most geomaterials are a complex matrix of fines and coarser particles, with distinct shapes and mineralogy interacting. This paper studied iron ore tailings over a broad range of pressures and stress histories to investigate the mechanical behavior of this nontextbook geomaterial. A thorough experimental program was conducted, and aspects of the stress–strain response, yielding, hardening, and critical state were evaluated. The state boundary surface of iron ore tailings also was investigated. The results demonstrated that the stress history of tailings affects the tailings' behavior only at elevated stress levels. The existence of particles with distinct mineralogy in the iron ore tailings (mainly iron oxide and quartz) could have induced different breakage patterns, with an evolving particle morphology being the dominant mechanism up to the pressures achieved. [ABSTRACT FROM AUTHOR]

It is well known that a complex circulant matrix can be diagonalized by a discrete Fourier matrix with imaginary unit i. The main aim of this paper is to demonstrate that a quaternion circulant matrix cannot be diagonalized by a discrete quaternion Fourier matrix with three imaginary units i, j, and k. Instead, a quaternion circulant matrix can be block-diagonalized into 1-by-1 block and 2-by-2 block matrices by permuted discrete quaternion Fourier transform matrix. With such a block-diagonalized form, the inverse of a quaternion circulant matrix can be determined efficiently similarly to the inverse of a complex circulant matrix. We make use of this block-diagonalized form to study quaternion tensor singular value decomposition of quaternion tensors where the entries are quaternion numbers. The applications, including computing the inverse of a quaternion circulant matrix and solving quaternion Toeplitz systems arising from linear prediction of quaternion signals, are employed to validate the efficiency of our proposed block-diagonalized results. [ABSTRACT FROM AUTHOR]

The multiparameter matrix pencil problem (MPP) is a generalization of the one-parameter MPP: given a set of r + 1, m x n complex matrices A0,...,Ar, with m ≥ n + r - 1, it is required to find all complex scalars λ0,...,λr, not all zero, such that the matrix pencil A(λ) = ... = 0λiAi loses column rank and the corresponding nonzero complex vector x such that A(λ)x = 0. We call the (r+1)-tuple λ0,...,λr an eigenvalue and the corresponding vector x an eigenvector. This problem is related to the well-known multiparameter eigenvalue problem except that there is only one pencil and, crucially, the matrices are not necessarily square. This paper uses our preliminary investigation in F. F. Alsubaie [H2 Optimal Model Reduction for Linear Dynamic Systems and the Solution of Multiparameter Matrix Pencil Problems, PhD thesis, Imperial College London, 2019], which presents a theoretical study of the multiparameter MPP and its applications in the H2 optimal model reduction problem, to give a full solution to the two-parameter MPP. First, an inflation process is implemented to show that the two-parameter MPP is equivalent to a set of three m² x n² simultaneous one-parameter MPPs. These problems are given in terms of Kronecker commutator operators (involving the original matrices) that exhibit several symmetries. These symmetries are analyzed and are then used to deflate the dimensions of the one-parameter MPPs to ... x ..., thus simplifying their numerical solution. In the case in which m = n + 1, it is shown that the two-parameter MPP has at least one solution and generically ... solutions, and furthermore that, under a rank assumption, the Kronecker determinant operators satisfy a commutativity property. This is then used to show that the two-parameter MPP is equivalent to a set of three simultaneous eigenvalue problems of dimension ... x .... A general solution algorithm is presented and numerical examples are given to outline the procedure of the proposed algorithm. [ABSTRACT FROM AUTHOR]

This paper focuses on the solution of the reduced biquaternion equation AX+XB = C using the E-extra iteration method. By utilizing the complex decomposition of a reduced biquaternion matrix, we transform the equation into a complex matrix equation. Subsequently, we analyze the convergence of this method and provide guidelines for selecting optimal parameters. Finally, numerical examples are presented to demonstrate the efficacy of our algorithm. [ABSTRACT FROM AUTHOR]

This paper is devoted to dealing with the issue of the estimation of the domain of attraction (DOA) for highly nonlinear neutral complex networks (HNNCNs) with time delays. Firstly, by the Razumikhin approach, we establish several novel lemmas on the estimation of DOA for highly nonlinear neutral differential systems. The cases of bounded non-differentiable delays and unbounded proportional delays are discussed, respectively. Subsequently, by utilizing the proposed lemmas, combining the Lyapunov stability theory and inequality technique, the estimation of DOA on HNNCNs with bounded delays or proportional delays is derived when the chosen control gain is sufficiently large. If initial values start from DOA, then the states of systems will exponentially or polynomially converge to the equilibrium point, which means that the local exponential or polynomial synchronization of HNNCNs is realized. Additionally, the weighted outer-coupling matrix of complex networks is not required to be symmetric, which means that the derived results can be applied to both the undirected networks and directed networks. Finally, several numerical examples are provided to illustrate the feasibility of theoretical findings. [ABSTRACT FROM AUTHOR]