Linear Response Research Articles

Screen-printed electrodes decorated with low content Pt–Ni microstructures for sensitive detection of Zn(II), ascorbic acid and paracetamol in pharmaceutical products and human blood samples

In this study, we report for the first time, a method for simultaneous detection of paracetamol (PA) and its toxic impurities, 4-aminophenol (4-AP), as well as commonly co-formulated drugs, ascorbic acid and zinc (AA and Zn(II)), using screen-printed electrodes (SPEs) as a sensing platform. To improve the electrochemical performance of the SPEs, these are decorated with platinum and nickel microstructures (Pt–Ni), using a simple electrodeposition technique. The structures and morphologies of the synthesized Pt–Ni/SPE electrode were confirmed by FE–SEM, TEM, EDX, XRD and AFM measurements. Furthermore, electrochemical characterization of the as-prepared sensor was investigated using cyclic voltammetry and electrochemical impedance spectroscopy methods. Under optimum conditions, the content of 4-AP, PA, AA and Zn(II) was quantified using cyclic voltammetry, differential pulse voltammetry and square-wave voltammetry techniques. The designed sensor exploits a dual effect, leveraging the efficiency of Pt for Zn(II) detection and Pt–Ni for the detection of 4-AP, AA, and PA. On one hand the as-prepared Pt–Ni/SPE sensor exhibits a linear response towards 4-AP and PA, ranging from 0.5 to 200 μM for both, with detection limits of 0.33 µM and 0.23 µM (S/N = 3) for 4-AP and PA, respectively. On the other hand, it demonstrates a linear response towards PA, AA, and Zn(II), ranging from 0.01 to 0.8 μM for Zn(II), 10 to 1800 μM for AA, and 0.5 to 200 μM for PA, with detection limits of 0.004 µM, 9.0 µM, and 0.15 µM for Zn(II), AA, and PA, respectively. Crucially, the as-fabricated sensor, with its remarkable reproducibility, recovery, long-term stability, and anti-interference capabilities, effectively quantified 4-AP, PA, Zn(II) and AA in both pharmaceutical formulations and human plasma samples.

SWCNT fibers decorated with Au nanoparticles as voltammetric sensors for arsenic (III) determination

We developed a new method to produce fiber electrodes from single-walled carbon nanotube (SWCNT) films, which can be employed as a novel sensing platform for electrochemical investigations and analysis. By assembling SWCNT bundles in the form of a strong free-standing fiber with almost entire surface accessible to an analyte, we are able to avoid the interference of substrate and improve detection efficiency. We examined the influence of physical, chemical and electrochemical pretreatments of the new electrode SWCNT material on its properties. Transmission and scanning electron microscopy, Raman spectroscopy and cyclic voltammetry were used to characterize the SWCNT fibers. The modification of the SWCNT fiber electrode with gold nanoparticles provides the necessary analytical characteristics including high repeatability and sensitivity and low detection limit (1.3 – 2.1 μg L-1) for arsenic determination by anodic stripping voltammetry. Arsenic detection parameters such as deposition potential, deposition time and scan rate were optimized. Linear responses were found in concentration ranges from 3 to 210 μg L-1 and 7 to 125 μg L-1 for gold modified SWCNT fiber sensors (the SWCNTs were synthesized using CO or ethanol as precursors) at a relatively low deposition time of 60 s. The developed Au-SWCNT sensors allow rapid As determination in real samples and exhibit high durability and long service life.

A novel gas sensor based on ZnO nanoparticles self-assembly porous networks for morphine drug detection in methanol

Developing efficient drug-detecting technologies is critical to the fight against their related abuse and trafficking crimes. In the present work, a novel morphine detection device based on metal-oxide-semiconductor (MOS) gas sensors with low-cost, highly sensitive, and portable is designed and fabricated. The exclusive sensitive material, ZnO nanoparticles self-assembly porous networks (ZnO-N) with ample oxygen vacancies (OV) defects prepared by PVP-chelated precipitation followed by a chemical blowing calcination method, is decisive to morphine drug identification. OV defects can modulate the intrinsic electronic structure and endow ZnO-N with more suitable band structures for enhancing oxygen species adsorption and morphine molecules oxidation. The optimal ZnO-N-2 sensor exhibits positive linear relationship response values of 1.1–8.8 in the concentrations of 2–200 ppm toward the standard morphine drug sample at the optimal operating temperature of 250°C. More importantly, the homemade portable device equipped with the ZnO-N-2 sensor can accurately identify the morphine drug and perform early warning. This work innovatively demonstrates the feasibility of MOS gas sensors for the detection of stashing morphine drugs in methanol, which is of great significance for effectively combating global drug-related crimes.

Linear and fractional response for nonlinear dissipative SPDEs

Linear and fractional response for nonlinear dissipative SPDEs

A ‘‘Turn-on’’ Al(III)-Mediated Fluorescent Micro-Probe for Quercetin Sensing

Quercetin (Qr) is a common flavonoid widely found in plants with promising pharmacological activities. It is thus worthwhile to design a convenient method for its detection. In this work, a specific Al3+-regulated poly(cyclotriphosphazene-co-curcumin) (PC-Al) micro-probe was designed for real-time detection of Qr, therein significant “turn-on” fluorescence was observed after addition of Qr to PC-Al. Under optimal conditions, the probe has a detection limit of 23.2 nM for Qr sensing with good linearity in the range of 0–5 × 10−5 M. Moreover, real-time applications of the PC-Al probe in red wine, orange juice, and honey samples were validated. Furthermore, assisted by a consumer smartphone sensing platform, the sensor shows an excellent linear response between the red/blue ratio (R/B) of the two color channels in the picture and the concentration of Qr in the range of 1–120 μM, achieving quantitative detection of Qr. The introduction of smartphone system to realize convenient detection of Qr demonstrates good application prospects of this Al3+-mediated fluorescence probe.

Molecular imprinting electrochemical sensor based on hollow spherical PProDOT-2CH2OH and chitosan-derived carbon materials for highly sensitive detection of chloramphenicol

The misuse of chloramphenicol (CAP) has jeopardized environmental safety. It is critical to create an effective and sensitive CAP detection technique. In this paper, a composite of chitosan (CS)-derived carbon material modified hollow spherical hydroxylated poly(3,4-propylenedioxythiophene) (PProDOT-2CH2OH) was designed, which innovatively used o-phenylenediamine and p-aminobenzoic acid as bi-functional monomers to prepare molecular imprinting polymer (MIP) sensors for highly sensitive analysis and determination of CAP. It was found that the hollow spherical structure of PProDOT-2CH2OH significantly enhanced the rapid electron migration. When combined with the CS-derived carbon material, which has multi-functional sites, it improved the electrical activity and stability of the sensor. It also provided more active centers for the MIP layer to specifically recognize CAP. Therefore, this MIP sensor had a wide linear response (0.0001 ∼ 125 μM), a low limit of detection (LOD, 6.6 pM), excellent selectivity and stability. In addition, studies showed that the sensor has potential practical value. Environmental implicationChloramphenicol (CAP) is one of the most widely used antibiotics with the highest dosage due to its low price and broad-spectrum antimicrobial properties. Due to its incomplete metabolism in living organisms and its difficulty in degrading in the environment, contamination caused by it can pose a threat to public health. In this study, a novel molecularly imprinted sensor (MIP/PC2C1/GCE) was designed to provide a new idea for rapid and precise removal of CAP by adsorption. The detection of CAP in pharmaceutical, water quality, and food fields was realized.

Cross-Priming-Linked Hierarchical Isothermal Amplification Programming Progressive Activating Clustered Regularly Interspaced Short Palindromic Repeats/Cas12a in miRNA Signaling.

Cascade isothermal nucleic acid amplification, which integrates several different amplification protocols to enhance the assay performance, is widely utilized in biosensing, particularly for detecting microRNAs (miRNAs), crucial biomarkers associated with tumor initiation and progression. However, striking a balance between a high amplification efficiency and simplicity in design remains a challenge. Therefore, methods achieving high amplification efficiency without significantly increasing complexity are highly favored. In this study, we propose a novel approach for miRNA detection, employing cross-priming-linked hierarchical isothermal amplification (CP-HIA) to progressively activate the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas12a system. The CP-HIA method strategically combines nicking-rolling circle amplification (n-RCA) and palindrome-aided circular strand displacement amplification (p-CSDA) for miRNA detection. Remarkably, this method utilizes only two main probes. Its key innovation lies in the interactive cross-priming strategy, wherein the amplification product from n-RCA is recycled to further drive p-CSDA, and vice versa. This interactive process establishes a hierarchical amplification, significantly enriching the activation probes for progressive CRISPR/Cas12a activation and subsequent target signal amplification. Consequently, the method exhibits greatly enhanced analytical performance, including high sensitivity and specificity in detecting low concentrations of miRNA. As low as 1.06 fM miRNA can thus be quantitatively detected, and the linear response of the miRNA is from 10 fM to 10 nM. These features demonstrate its potential for early disease diagnosis and monitoring. We anticipate that the CP-HIA method will serve as a promising platform for developing advanced molecular diagnostic tools for biomedical research.

Exploring γ and UV irradiation responses on thermoluminescence and optical thermometry studies on Y4Al2O9:Ho3+ nanophosphor

A series of green emitting Ho3+ (1–9 mol%) doped Y4Al2O9 nanophosphors (NPs) are synthesized via solution combustion technique. Photoluminescence (PL) studies shows emission peaks recorded at ∼ 522 nm (5F3→5I8), 545 (5F4, 5S2→5I8), 659 (5F5→5I8) and 730 (5F4→5I7) upon excited at 460 nm wavelength. With a tremendous potential for application in white light-emitting diodes (w-LEDs), the phosphors show a bright green emission under 460 nm excitation. They also have a notable activation energy (0.31 eV), high color purity (98.2 %), and a remarkable quantum yield (87.1 %). Most astonishingly, even at temperatures as high as 420 K, YAO:5Ho3+nanoparticles retain 88.9 % of their initial fluorescence intensity. Using the fluorescence intensity ratio (FIR) method, the temperature sensing potential is also investigated. Thermoluminescence (TL) glow curves of γ (1 kGy) and UV (1 h) irradiated YAO:Ho3+(1–9 mol%) NPs exhibit two glow curves and highest intensity is recorded for YAO:5Ho3+NPs. TL characteristics of 5 mol% Ho3+ doped YAO NPs are subjected to γ (1 Gy-5 kGy) and UV (0.25–6 h) irradiation. Two glow curves recorded at 475 K (major peak) and 567 K (shouldered peak) for γ irradiation. However, for UV irradiation two glow curves at 478 K (major peak) and 575 K (shouldered peak) are recorded utilizing a 5 °C per minute heating rate. TL intensity varies with γ and UV exposure is recorded for optimized NPs and major glow peaks showcase linear response for both γ and UV irradiations, indicating that the prepared phosphor can be used in TL personal dosimetry. Furthermore, compared to γ-irradiated phosphor, UV-irradiated phosphor shows greater fading. The overall results clearly demonstrate that the optimized phosphor has proven to be an outstanding candidate for multifunctional applications.

Exploring the viability of desiccant silica gel beads as A novel material for radiation dosimetry: A preliminary investigation

Silica gel bead material, with its porous structure, high surface area, uniform particle size, stability, and excellent adsorption capacity, is a key material for advancing dosimeter technologies. These qualities make it ideal for accurately measuring and monitoring ionizing radiation in various environments. The research aims to characterize the response of different ionizing radiation sources on desiccant silica gel beads, laying the groundwork for potential applications in medical dosimetry. In this study, silica gel bead samples were subjected to various radiation sources, including gamma rays with an average energy of 1.25 MeV, photons (6 MV), and electrons (6 MeV). The radiation was administered at doses within the range of 2 Gy–20 Gy, which is commonly used in radiotherapy to evaluate the dosimetric behaviour of the desiccant silica gel bead samples using the conventional thermoluminescence (TL) technique. The silica gel bead samples have been found to provide a highly linear dose response within the dose range of interest, with the coefficient of determination (R2) ranging between 0.91 and 0.96. Additionally, the samples show high sensitivity at lower doses and maintain excellent reproducibility, with a standard deviation of less than 4%. In regard to fading evaluation, desiccant silica gel beads exhibit minimal signal loss within 35 days post-irradiation, averaging between 20% and 38%. The findings of this study are promising for developing a new dosimeter, which will enhance radiation monitoring and measurement practices in various environments. These improvements cover dosimetric applications in medical and industrial fields including food safety and agricultural development.

Numerical Analysis of a Linear Quasi-Static and Vibrational Response of Gypsum Sandwich Panels Reinforced with Fiberglass Fabrics

Numerical Analysis of a Linear Quasi-Static and Vibrational Response of Gypsum Sandwich Panels Reinforced with Fiberglass Fabrics

Development of Novel Surface-Enhanced Raman Spectroscopy-Based Biosensors by Controlling the Roughness of Gold/Alumina Platforms for Highly Sensitive Detection of Pyocyanin Secreted from Pseudomonas aeruginosa.

Pyocyanin is considered a maker of Pseudomonas aeruginosa (P. aeruginosa) infection. Pyocyanin is among the toxins released by the P. aeruginosa bacteria. Therefore, the development of a direct detection of PYO is crucial due to its importance. Among the different optical techniques, the Raman technique showed unique advantages because of its fingerprint data, no sample preparation, and high sensitivity besides its ease of use. Noble metal nanostructures were used to improve the Raman response based on the surface-enhanced Raman scattering (SERS) technique. Anodic metal oxide attracts much interest due to its unique morphology and applications. The porous metal structure provides a large surface area that could be used as a hard template for periodic nanostructure array fabrication. Porous shapes and sizes could be controlled by controlling the anodization parameters, including the anodization voltage, current, temperature, and time, besides the metal purity and the electrolyte type/concentration. The anodization of aluminum foil results in anodic aluminum oxide (AAO) formation with different roughness. Here, we will use the roughness as hotspot centers to enhance the Raman signals. Firstly, a thin film of gold was deposited to develop gold/alumina (Au/AAO) platforms and then applied as SERS-active surfaces. The morphology and roughness of the developed substrates were investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The Au/AAO substrates were used for monitoring pyocyanin secreted from Pseudomonas aeruginosa microorganisms based on the SERS technique. The results showed that the roughness degree affects the enhancement efficiency of this sensor. The high enhancement was obtained in the case of depositing a 30 nm layer of gold onto the second anodized substrates. The developed sensor showed high sensitivity toward pyocyanin with a limit of detection of 96 nM with a linear response over a dynamic range from 1 µM to 9 µM.

Hollow-like three-dimensional structure of methyl orange-delaminated Ti3C2 MXene nanocomposite for high-performance electrochemical sensing of tryptophan.

Tryptophan(Trp) is being explored as a potential biomarker for various diseases associated with decreased tryptophan levels; however, metabolomic methods are expensive and time-consuming and require extensive sample analysis, making them urgently needed for trace detection. Toexploit the properties of Ti3C2 MXenes a rational porous methyl orange (MO)-delaminated Ti3C2 MXene was preparedvia a facile mixing process for the electrocatalytic oxidation of Trp. The hollow-like 3D structure with a more open structure and the synergistic effect of MO and conductive Ti3C2 MXene enhanced its electrochemical catalytic capability toward Trp biosensing. More importantly, MO can stabilize Ti3C2 MXene nanosheets through noncovalent π-π interactions and hydrogen bonding. Compared with covalent attachment, these non-covalent interactions preserve the electronic conductivity of the Ti3C2 MXene nanosheets. Finally, the addition of MO-derived nitrogen (N) and sulfur (S) atoms to Ti3C2 MXene enhanced the electronegativity and improved its affinity for specific molecules, resulting in high-performance electrocatalytic activity. The proposed biosensor exhibited a wide linear response in concentration ranges of 0.01-0.3 µM and 0.5-120 µM, with a low detection limit of 15 nM for tryptophan detection, and high anti-interference ability in complex media of human urine and egg white matrices. The exceptional abilities of the MO/Ti3C2 nanocatalyst make it a promising electrode material for the detection of important biomolecules.

Validity of the constant relaxation time approximation in topological insulator: Sn-BSTS a case study

Gate-voltage dependent quantum oscillations in topological insulator Sn0.02Bi1.08Sb0.9Te2S (Sn-BSTS) are analyzed on the basis of the Lifshitz−Kosevich theory. The angular dependence of the quantum oscillations and Landau-level fan diagram analysis show that the quantum oscillations originate from topological surface states with the Berry phase of π. Gate-voltage control allows precise control of the Fermi energy, and a very weak energy dependence of the relaxation time τ of the topological surface states is revealed. By a simple algebraic argument using the linear response theory, it is shown that the weak energy dependence of τ validates the constant relaxation time approximation [τE,T=τ0] in the calculation of the Seebeck coefficient S and zTel=σS2T/κel.

Fluctuation effects in superconducting nanowires under electric field

This study applies the time-dependent Ginzburg–Landau (TDGL) theory with thermal noise to analyze the thermoelectric and transport properties of superconducting Sn nanowires, focusing on the thermopower (αxx) and the phase transition characteristics in the S-shaped J-E curves. We observe significant contributions from superconducting Cooper pairs, which remain nonzero above the critical temperature (Tc), indicating residual superconductivity due to strong thermal fluctuations. The S-like shape in the J-E curves is attributed to a dynamical instability transition temperature (T∗) at approximately 2.9 K, where thermal fluctuations dominate. Furthermore, we compare the resistance in the linear response to experimental data for Sn nanowires both below and above Tc. Below Tc, the resistance sharply decreases, reflecting the robust superconducting state, while above Tc, it increases, aligning with normal state behavior. In nonlinear response case, our results indicate that high electric fields can be effectively used to suppress order-parameter fluctuations and the electrical conductivity in superconducting nanowires. The findings provide critical insights into the thermoelectric behavior and phase transitions in Sn nanowires, highlighting the importance of Cooper pair dynamics in shaping the transport properties of one-dimensional superconductors. This understanding is essential for the development of advanced nanoelectronic devices leveraging these unique superconducting properties.

Development of MOF-derived Co3O4 microspheres composed of fiber stacks for simultaneous electrochemical detection of Pb2+ and Cu2+

As an ideal transition metal oxide, Co3O4 is a P-type semiconductor with excellent electrical conductivity, non-toxicity and low cost. This work reports the successful construction of Co3O4 materials derived from metal-organic frameworks (MOFs) using a surfactant micelle template-solvothermal method. The modified electrodes are investigated for their ability to electrochemically detect Pb2+ and Cu2+ in aqueous environments. By adjusting the mass ratios of alkaline modifiers, the morphological microstructures of Co3O4-X exhibit a transition from distinctive microspheres composed of fiber stacks to rods. The results indicate that Co3O4-1(NH4F/CO(NH2)2 = 1:0) has a distinctive microsphere structure composed of stacked fibers, unlike the other two materials. Co3O4-1/GCE is used as the active material of the modified electrode, it shows the largest peak response currents to Pb2+ and Cu2+, and efficiently detects Pb2+ and Cu2+ in the aqueous environment individually and simultaneously. The linear response range of Co3O4-1/GCE for the simultaneous detection of Pb2+ and Cu2+ is 0.5–1.5 μM, with the limits of detection (LOD, S/N = 3) are 9.77 nM and 14.97 nM, respectively. The material exhibits a favorable electrochemical response, via a distinctive Co3O4-1 microsphere structure composed of stacked fibers. This structure enhances the number of active adsorption sites on the material, thereby facilitating the adsorption of heavy metal ions (HMIs). The presence of oxygen vacancies (OV) can also facilitate the adsorption of ions. The Co3O4-1/GCE electrode also exhibits excellent anti-interference ability, stability, and repeatability. This is of great practical significance for detecting Pb2+ and Cu2+ in real water samples and provides a new approach for developing high-performance metal oxide electrochemical sensors derived from MOFs.Graphical abstract

A self-powered sensor based on hollow bimetallic sulfide and double-strand TSDR amplification achieves sensitive miRNA-21 detection

MicroRNA (miRNA) sensitive detection is significant for cancer diagnosis. Currently, self-powered biosensors in clinical miRNA detection show the advantages of no external power supply, mild reaction conditions, low cost and portability. In this work, the bimetallic sulfide heterojunction hollow nanocubes are prepared as the substrate material, which can significantly improve the electrochemical reaction rate and increase the enzyme load. Meanwhile, we design the independent duplex-chain assisted toehold mediated strand displacement reaction (TSDR) strategy. The two substable double chains trigger a continuous chain displacement reaction, and the current signal amplification is realized based on molecular recognition. The constructed sensor has a linear response range of 0.05–10000 fM and a detection limit (LOD) of 8.3 aM. In addition, we use commercial apps to present signals, fundamentally changing the signal output mode of electrochemical sensors, and facilitating the construction of a portable real-time sensor platform. The self-powered biosensor has the characteristics of good biocompatibility, real-time monitoring and economic efficiency in miRNA detection, which provides a new idea for sensitive detection of miRNA. Moreover, it has far-reaching reference significance for the development of other sensing technologies, which is expected to extend from the medical field to environmental monitoring, food safety and other fields.

CuO-ZIF-8 modified electrode surface as a new electrochemical sensing platform for detection of free chlorine in aqueous solution

This work has applied metal–organic frameworks (MOFs) with high adsorbability and catalytic activity to develop electrochemical sensors to determine free chlorine (free-Cl) concentrations in aqueous media. A zeolitic imidazolate frameworks, Zn(Hmim)2 (ZIF-8) has been synthesized and incorporated with CuO nanosheets to decorate a glassy carbon electrode (GCE) and provide a new sensor for free-Cl determination. The as-prepared ZIF-8 and CuO-ZIF-8 composites have been characterized by FESEM, EDX, XRD, and FT-IR analyses. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) utilized to characterize the CuO-ZIF-8/GC modified electrode electrochemically, demonstrated the ability of the sensor to measure free-Cl concentration. Using differential pulse voltammetry (DPV) and under the optimal conditions, the prepared CuO-ZIF-8/GC modified electrode showed a linear response in the 0.25–60 ppm range with a 12 ppb detection limit (LOD) for free-Cl concentration. Finally, the fabricated sensor was applied to analyze free-Cl from actual swimming pool water samples with promising 97.5 to 103.0% recoveries.

Oscillatory Interactions between Colloidal Particles in Polyelectrolyte Solutions: Linear Response Theory

Oscillatory Interactions between Colloidal Particles in Polyelectrolyte Solutions: Linear Response Theory

PKa Calculations of GPCRs: Understanding Protonation States in Receptor Activation.

The increase in the available G protein-coupled receptor (GPCR) structures has been pivotal in helping to understand their activation process. However, the role of protonation-conformation coupling in GPCR activation still needs to be clarified. We studied the protonation behavior of the highly conserved Asp2.50 residue in five different class A GPCRs (active and inactive conformations) using a linear response approximation (LRA) pKa calculation protocol. We observed consistent differences (1.3 pK units) for the macroscopic pKa values between the inactive and active states of the A2AR and B2AR receptors, indicating the protonation of Asp2.50 during GPCR activation. This process seems to be specific and not conserved, as no differences were observed in the pKa values of the remaining receptors (CB1R, NT1R, and GHSR).

Printed potentiometric, non-enzymatic sensors based on Zr(IV)-porphyrins for determination of lactate

The feasibility of using Zr-porphyrins as ionophores selective towards lactate ions was examined. Zr-tetraphenylporphyrin (Zr-TPP) and Zr-octaethylporphyrin (Zr-OEP) were tested in polyurethane membranes plasticized with dioctyl sebacate or o-nitrophenyl ether and containing cationic or anionic lipophilic sites, respectively. The best lactate response characteristics were registered for membrane plasticized with dioctyl sebacate and doped with Zr-TPP and cationic lipophilic sites. Classical electrodes with this membrane showed high selectivity towards lactate ions with a sensitivity of −76.6 mV dec−1 and linear lactate calibration range from 10−4 M to 10−1 M. Polymeric membranes containing Zr-TPP were then drop-casted on screen-printed transducers with electrodes made of graphene-containing paste. It was found that the potentiometric behavior of these miniature planar sensors is very similar to classical electrodes. In the next step, fully printed sensors, with both graphene electrodes and ion-selective polymeric membranes, were fabricated using aerosol jet printing. The sensitivity of these electrodes towards lactate was −79.01±0.39 mV dec−1 with a linear response range from 10−3.5 M to 10−1 M and a fast response to lactate concentration changes. The proposed electrode demonstrates a rare example of a potentiometric, non-enzymatic sensor for the determination of lactate ions, with the possibility of miniaturization and mass fabrication using printing methods.