Limit Of Detection Values Research Articles

GREEN ANALYTICAL TECHNIQUES FOR THE ESTIMATION OF RALTEGRAVIR IN DRUG AND PHARMACEUTICALS

Objectives: The objective of this study was to develop and validate a green solvent-assisted chromatographic method for the detection of raltegravir in bulk and pharmaceutical formulations. The study aimed to ensure an environmentally sustainable approach while maintaining precision, accuracy, and regulatory compliance. Methods: A chromatographic method was developed using ethanol and aqueous amine buffer (85:15%v/v) as the mobile phase at pH 4.0. The method was optimized with a flow rate of 1.0 mL/min, and the compound was detected at 247 nm. Validation was conducted following the International Council for Harmonization (ICH) guidelines, assessing key parameters such as linearity, limit of detection (LOD), limit of quantification (LOQ), and forced degradation studies. The greenness of the method was evaluated using various green chemistry assessment tools, including the Analytical GREEnness Approach (AGREE), green analytical procedure index (GAPI), Complex GAPI, red analytical performance index, blue applicability grade index, and Red Green Blue (RGB) assessment models. Results: The developed method achieved a retention time of 5.46 min and exhibited a strong linear relationship with a correlation coefficient (r²) of 0.999 within the concentration range of 3.0–15 μg/mL. The LOD and LOQ values were within acceptable criteria, demonstrating the method’s sensitivity. The greenness assessment revealed that the AGREE score was close to 1, while hexagonal charts with green centers confirmed the eco-friendliness of the method in comparison to reported conventional techniques. Forced degradation studies indicated acceptable degradation levels ranging from 5% to 20%, in compliance with ICH Q1B guidelines, ensuring the method’s robustness and stability-indicating capability. Conclusion: The proposed green solvent-assisted chromatographic method provides an eco-friendly, precise, and accurate approach for the analysis of raltegravir in bulk and pharmaceutical formulations. The method aligns with green analytical chemistry principles and regulatory guidelines, offering a sustainable alternative to conventional chromatographic techniques.

Development of low cost ZnO based chemi resistive biosensor for the detection of vitamin B6 mediated by quantum dots

In this study, we developed a chemi-resistive sensor for vitamin B6 mediated by CdTe quantum dots (Cadmium Telluride QDs) utilizing ZnO-based thin films through the spin-coating sol–gel technique annealed at 500 °C. The sensor successfully recognized vitamin B6 (Pyridoxine) in concentrations ranging from 2 to 10 µM by employing CdTe quantum dots (Cadmium Telluride QDs) on the ZnO thin film. This detection was achieved by implementing an amperometric (I–V) method, typically operating at a working voltage below 2 V. From the slope of the calibration curve, the sensitivity, and the limit of detection values are estimated to be 7.56 ± 0.92 nA/µM and 0.906 µM (n = 5), respectively. This study conducted electrochemical impedance spectroscopy (EIS) in conjunction with current–voltage (I–V) measurements. The results obtained from EIS are consistent with the current response observed in the I–V measurements. The sensing mechanism primarily relies on the charge transfer phenomenon (electrostatic attraction) between the analyte (vitamin B6 mediated by CdTe quantum dots) and the ZnO thin film. In summary, our work introduces a simple, rapid, and cost-effective ZnO thin film-based sensing device for detecting vitamin B6, mediated by CdTe QDs. This sensor holds promise for a wide range of applications, from pharmaceutical quality control to point-of-care diagnostics and routine vitamin B screening.

A Hydrophillic Deep Eutectic Solvent Assisted Magnetic Colloidal Gel Based Dispersive Solid Phase Microextraction Method for Preconcentration of Brown HT (E155)

A hydrophillic deep eutectic solvent assisted magnetic colloidal gel based dispersive solid phase microextraction method (MCG-dSPME) was developed for the pre-concentration of Brown HT (E155) before its spectrophotometric analysis. Magnetic colloidal gel was obtained from Fe3O4@XAD-7 nanoparticles and phenol/choline chloride (2:1) (hyrophillic deep eutectic solvent (DES). For the optimization of the developed method, several parameters such as pH, amount of Fe3O4@XAD-7 nanoparticles in the colloidal gel, volume of colloidal gel, type of desorption solvent, vortex time (for adsorption and desorption), sample volume were investigated. After determining the optimum conditions, the linear range, limit of detection (LOD), enhencament factor (EF), preconcentration factor (PF), relative standard deviation (RSD %) of the method were calculated. Then, addition/recovery test and intraday-interday test were applied for the accuracy and the precision, respectively. The matrix effect study was examined for the selectivity of the method. The linear range, LOD, RSD %, EF, and PF values of the method were found to be 0.05-0.75 mgL-1, 0.016. mgL-1, 3.8%, 51 and 25, respectively. The study was found to be no interference method with high accuracy and precision. In this study, according to our literature research, since there are very few studies on the determination of Brown HT, it was aimed to develop an up-to-date, economical, non-invasive, environmentally friendly and simple method for this dye.

Rapid Detection of Perfluorodecanoic Acid and Perfluorooctanesulfonic Acid in Foods Using a Molecularly Imprinted Poly(o-phenylenediamine)/Modified Glassy Carbon Electrode.

In the current work, a modified glassy carbon electrode (GCE) with excellent conductivity was prepared by drop-coating carboxymethyl cellulose (CMC) and multiwalled carbon nanotubes (MWCNTs) on the GCE surface. On this basis, two highly selective molecularly imprinted sensors (MIP@PFDA/modified GCE and MIP@PFOS/modified GCE) were separately obtained by in situ electropolymerization of o-phenylenediamine (o-PD) with perfluorodecanoic acid (PFDA) and perfluorooctanesulfonic acid (PFOS) as templates. Under optimal conditions, sensitive quantification methods in the linearity ranges 0.1-1000 ng/mL (PFDA) and 0.05-900 ng/mL (PFOS) were developed via differential pulse voltammetry using [Fe(CN)6]3-/4- as a redox probe. The detection limit values of PFDA and PFOS were as low as 0.041 and 0.015 ng/mL, respectively. Both sensors also presented great stability and selectivity in coexistence with other interferences. Lastly, three food samples were utilized to verify the validity and applicability with recoveries of 89.97%-112.27%, confirming its potential for per- and polyfluoroalkyl substances (PFASs) monitoring in a complex matrix.

CeO2 Nanocubes as an Electrochemical Sensing Platform for Simultaneous Detection of Dopamine and Acetaminophen

The overlapping redox potentials of analytes and the lack of selectivity present significant challenges for unmodified electrodes in electrochemical sensing. In this work, we have fabricated an electrochemical sensor based on cerium oxide nanocubes (CeO2-NCs) coated glassy carbon electrode (CeO2-NCs@GCE) for individual and simultaneous detection of dopamine (DA) and acetaminophen (APAP) with high sensitivity and selectivity. The CeO2-NCs were synthesized using a one-step hydrothermal method and characterized by Transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and Raman spectroscopy. Cyclic voltammetry and electrochemical impedance spectroscopy were employed for electrochemical characterizations. With improved electrocatalytic redox activity due to enhanced active surface area and reduced interfacial charge transfer resistance, CeO2-NCs@GCE shows superior detection efficiency. The detection of DA and APAP was evaluated using differential pulse voltammetry. Low detection limit values of 0.696 μM for DA and 0.341 μM for APAP with a wide linear range of 10–400 μM applicability were achieved. The CeO2-NCs@GCE sensor was also used to detect DA in DA injection and APAP in paracetamol tablet samples. The developed sensor demonstrated satisfactory recovery results ranging from 96.5 to 102.8% in pharmaceutical samples, confirming the applicability of the proposed method for simultaneous detection of DA and APAP in real samples.

Comparison of approaches for assessing detection and quantitation limits in bioanalytical methods using HPLC for sotalol in plasma

The limit of detection (LOD) and limit of quantification (LOQ) stand elements in the validation of analytical and bioanalytical methods as emphasized in numerous guidelines. Despite this, the absence of a universal protocol for establishing these limits has led to varied approaches among researchers and analysts in literature. In this work we present the latest graphical strategy of validation known as the uncertainty profile to assess the LOQ and LOD. Then, we conducted a comparative study of this approach with those based on accuracy profile and parameters of the calibration curve. We realize the uncertainty profile from the uncertainty parameter calculated from the tolerance interval. Furthermore, we provide a succinct overview of alternative methods for computing these limits. This includes the classical strategy based on statistical concepts and graphical one using the method of accuracy profile. In pursuit of this objective, these strategies are implemented in the same experimental results of an HPLC method dedicated for the determination of sotalol in plasma using atenolol as internal standard. The classical strategy based on statistical concepts provides underestimated values of LOD and LOQ. In the other side, the two graphical tools give a relevant and realistic assessment, and the values LOD and LOQ found by uncertainty and accuracy profiles are in the same order of magnitude, especially the method of uncertainty profile. It provides precise estimate of the measurement uncertainty. The graphical strategies of validation, uncertainty profile and accuracy profile, based on tolerance interval are a reliable alternative to the classic strategy, based on classical concepts, for assessment of LOD and LOQ.

Improvement and Application HPLC-UV Method for detecting of N-drugs in Pharmaceutical Formulations

The ultraviolet-visible high-performance liquid chromatography (HPLC–UV) coupled method was developed to detect five pharmaceutical compounds: indapamide (INDP), clomipramine (CMI), promethazine HCl (PMH), lisinopril (LSP) and trifluoperazine HCl (TFPH). The mobile phase consisted of 70% acetonitrile and 30% water, ensuring specific retention times (tR) for each compound. Analytical validation parameters were calculated from a calibration curve, including sensitivity, limit of detection (LOD) and linearity of the method. The LOD values of N-drugs were calculated as 6.24 μM for INDP, 2.19 for CMI, 10.57 for PMH, 6.68 for LSP and 1.25 for TFPH. Peak deconvolution or spectral deconvolution of standard solutions of drug mixtures was used to separate overlapping peaks in a dataset and extract information about individuals. Chromatographic separation of the standard mixture of pure compounds achieved a good resolution (R_s), ensuring the effective separation of the mixture components. However, other mixtures did not achieve satisfactory resolution due to retention time interference. Overall, the HPLC–UV method demonstrated good sensitivity and selectivity for the detection of the chosen pharmaceutical compounds. KEYWORDS Chromatogram, deconvolution, limit of detection, pharmaceutical analysis, retention time, sensitivity

Method development for simultaneous separation and identification of different therapeutic drugs by humic acid-based high performance liquid chromatographic column

Simultaneous quantitative and qualitative identification of drugs is an increasing demand by pharmaceutical industries. Present study deals with development of efficient, reliable and simultaneous separation of five drugs belonging to different therapeutic groups (i.e., Ornidazole (anti-bacterial/anti-fungal), Oxaprozin (anti-inflammatory), Fusidic acid (antibiotic), Pantoprazole and Omeprazole (acid reducers)) as first application by a newly developed humic acid appended aminopropyl silica filled chromatographic column. The extracted soil humic acid was immobilized on aminopropyl silica by amide bond formation. The material was characterized by fourier-transform infrared and scanning electron microscopic techniques. The separation method was developed by varying mobile phase composition, pH and flow rate, resulting optimum conditions were found to be 30% acetonitrile, 5.5 pH at 1 mL/min flow rate. Method was validated according to ICH guidelines. The results suggested higher accuracy, reproducibility, and linearity of column. Moreover, satisfactory values for limit of detection and limit of quantification justified the sensitivity of developed column. The column was successfully applied for determination of each drug in their commercial formulations. Finally, the efficiency of developed column was also compared with commercially available column. The results revealed that developed column is suitable for quality control and routine analysis of the cited drugs in their pharmaceutical dosage form.

Fast Determination of Fat-soluble Vitamins in Pharmaceutical Preparations by High-Performance Liquid Chromatography

Background: Vitamins are needed for the healthy functioning of the body. When these vitamins are not in sufficient amounts in the body, they are usually taken externally with pharmaceutical preparations. Taking vitamins into the body in the right amounts is possible by analyzing the amounts in pharmaceutical preparations with validated methods. Methods: In this study, a fast, simple, easily applicable, and selective normal-phase HPLC method was developed for the simultaneous determination of fat-soluble A, D3, E, and K1 vitamins in pharmaceutical preparations from syrup and tablets. Separation of the vitamins was carried out on a Zorbax CN column (250 x 4.6 mm, 5 µm) using a mixture of hexane-isopropyl alcohol (98:2, v/v) at 30°C column temperature and 1 ml/min flow rate. The detection wavelength is 280 nm. The developed method has been validated according to ICH Harmonised Tripartite Guideline Validation of Analytical Procedures: Text and Methodology Q2(R1) rules. Results: Calibration graphs are linear over the range of 10-1000 μg ml-1, 1-50 μg ml-1, 10-2000 μg ml-1, 0.5-20 μg ml-1, and the limit of detection values were found to be 1.496, 0.280, 1.388 and 0.040 μg ml-1 for A, D3, E and K1 vitamins, respectively. Relative standard deviation values, which express within-day and between-day repeatability, were found below 2.54%. Average recovery values were also found at about 100.28, 101.46, 100.65, and 100.29% for A, D3, E, and K1 vitamins, respectively. Conclusion: The developed and validated method was successfully applied to the simultaneous analysis of fat-soluble vitamins A, D3, E, and K1 in pharmaceutical preparations in syrup and tablet form.

A high-performance aptasensing interface based on pseudo-AuNBs@Ti3C2Tx MXene nanocomposite for non-invasive measurement of carbamazepine in human biofluids.

For the first time, a novel aptasensing interface based on smart integration of pseudo-gold nanobons (AuNBs) and Ti3C2Tx MXene isintroduced for high selective detection of carbamazepine (CBZ). The large specific surface area achieved from the proposed nanocomposite increases the targeted immobilization of the Apt sequence on the surface via AuNBs as the linkage. It embeds a high-performance grafting platform for trapping CBZ with high sensitivity and accuracy in human biofluids and pharmaceutical formulations. The molecular dynamic (MD) simulation method that exhibits how the Apt binds to CBZ in a conformation-switching assay format from a molecular view is a valid certification for the interaction of CBZ on the developed aptasensing interface. The aptasensor measured CBZ from 1 fM to 100 nM with a superior detection limit (LOD) value of 330 aM compared withother reported CBZ sensors. Due to using biocompatible and non-toxic compounds, consuming low energy and chemicals the greenness of the proposed strategy has been certified by the international scoring system.

Fano resonance-boosted topological sensor for next-generation sensing

The rapidly developing field of topological photonics has the potential to revolutionize the design and operation of optical systems. This study presents a novel approach for constructing a resilient sensor based on topological resonance. The coupling of the photonic crystal waveguide (PCW) with the topological corner state (TCS) within the structure forms the proposed sensor. The PCW provides a well-defined propagating mode, while the TCS is a localized mode that is topologically protected against perturbations. The coupling between the two modes contributes growth to a Fano resonance and results in a sharp and narrow spectral feature sensitive to the refractive index variation of the surrounding medium. The proposed sensor possesses a high sensitivity of ∼461.96 nm/RIU with a high Q-factor {10}^{6})$$\\end{document}]]>, high figure of merit {10}^{6}\\:{\ ext{R}\ ext{I}\ ext{U}}^{-1})$$\\end{document}]]>, and has an ideal detection limit value of. The present study gives a new platform for a more productive way of creating highly efficient topological Fano resonance sensors. The proposed sensor is resistant, sensitive, and highly versatile, making it beneficial for different applications.

Self-standing block shaped cobalt metal organic frameworks deposited graphite rod electrode for non-enzymatic electrochemical detection of imidacloprid in vegetable and fruit

Neonicotinoid pesticides are increasingly being used in agriculture and farming sectors, which can have hostile effects on the environment and water resources. All living creatures including humans had forcefully consumed from the environment this cancerous neonicotinoid pesticide, imidacloprid. Herein, our study reported a novel free-standing electrochemical sensor for ultrasensitive and discriminatory detection of imidacloprid (IM) pesticide using cobalt metal-organic framework (MOF) anchored graphite rod (GR). The surface structure and morphology of the porous Co(pyrazole dicarboxylic acid)[PZDA]MOFs were systematically investigated after solvothermal growth on graphite rods. Electrochemical experiments revealed noteworthy catalytic activity for Co(PZDA)MOF//GR in reducing imidacloprid. The synergistic effect between GRs and Co(PZDA)MOF significantly improves the electrochemical responses. Electrocatalysis studies displayed reversible diffusion-controlled kinetics of four electrons and four protons involved in the electro-reduction of imidacloprid. Detection of IM by differential pulse voltammetry (DPV) method portrays a wide lined dynamic range (0.01 – 100 µM) with a sensitivity of 83.69 μA μM−1 cm−2 and limit of detection value 4.8 nM. Moreover, Co(PZDA)MOF//GR electrode showed an unique electrocatalytic performance and excellent duplicability, outstanding repeatability, and brilliant storing steadiness up to two months. Thus, the sensor electrode provides a simple, affordable, environmentally friendly, cost-effective imidacloprid detection tool in real-world samples.

Quantitative determination of leptin hormone using gold nanoparticle-based lateral flow assay

A lateral flow assay (LFA) has been developed that can be used in point-of-care (PoC) use for the sensitive determination of leptin hormone. The limit of detection value was 0.158 ng/mL and the limit of quantification value was 0.479 ng/mL for leptin hormone. The stability studies showed that the assay response was equal to the initial value even after 6 months. LFA accuracy tests performed in commercial artificial serum samples were compared with the enzyme-linked immunosorbent assay (ELISA). The obtained recovery values between 95 and 110% show that the developed LFA can be used for quantitative determination of leptin hormone. As the result of the study, a fast and disposable assay was developed for the determination of leptin hormone, which can be performed with a small amount of sample in less than 15 min without the need for long-term analysis stages, qualified personnel, expensive equipment and devices.Graphical

Surface Engineered Nanoparticles Coupled with Pattern Recognition Techniques for Rapid Identification and Discrimination of Multiple Thiols in a Real Sample Matrix.

Thiols, including Cysteine (CYS) and Glutathione (GSH), play pivotal roles in numerous physiological processes as they are integral components of many essential biomolecules and are found abundantly in foods such as additives and antioxidants. Any deviations in thiol concentrations can disrupt normal physiological functions, affecting the body's metabolism and potentially leading to diseases such as Alzheimer's and Parkinson's diseases, etc. Consequently, the imperative need for developing reliable and robust techniques for thiol analysis is crucial for early disease detection and ensuring food safety. In this regard, we have decorated the surface of organic nanoparticles with metal ions, which have been characterized using various techniques such as Dynamic Light Scattering (DLS), Zeta potential, Fourier Transformation Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), and Transmission Electron Microscopy (TEM) and utilized for the detection and discrimination of various thiols (cysteine, Glutathione, 3-mercaptopropionic acid, 2-mercapto ethanol, and cysteamine). Photophysical results revealed that various thiols exhibit unique binding affinities toward sensor elements, serving as fingerprints for each thiol. These patterns can be quantitatively differentiated using linear discrimination analysis (LDA) and hierarchical clustering analysis (HCA). The sensor array effectively discriminates target thiols with 100% accuracy and high sensitivity with limit of detection values from 1.19 to 4.20 μM. Apparently, it offers required simplicity, rapid response, sensitivity, and stability, which holds promise for enhancing food safety.

Bright yellow fluorescent N-doped Ti3C2 MXene quantum dots as an "on/off/on" nanoprobe for selective As3+ ion detection.

Ti3C2 MXene quantum dots (MQDs) are considered to be an emerging nanomaterial in recent times, but the majority of MQDs exhibit limited emission properties in the blue-light region. Longer-wavelength emissive quantum dots are highly desirable in terms of various biological aspects including deep tissue penetration, superior signal-to-noise ratio, reduced radiation damage, etc. In this study, bright yellow fluorescent nitrogen-doped MQDs (N-MQDs) were successfully prepared using a one-pot hydrothermal method. The synthesized N-MQDs showed maximum emission at 570 nm upon excitation at a wavelength of 420 nm, with an optimum fluorescence quantum yield of 13.8%. Interestingly, the emission of the N-MQDs was significantly quenched upon the addition of As3+ ions. A mechanistic investigation revealed that static quenching was involved in the decrease in the fluorescence via the formation of a non-fluorescent complex due to the interaction of the functional groups of the N-MQDs and As3+. The quenched fluorescence was surprisingly recovered upon treatment of the complex with 2-amino-6-methoxybenzothiazole (MBTZ). The strong interaction of MBTZ with As3+ led to the detachment of the quencher from the N-MQDs, resulting in fluorescence recovery. The re-appearance of the functional groups of the N-MQDs after the addition of MBTZ was confirmed via spectroscopic study. Thus, the fluorescence "on/off/on" phenomenon of the N-MQDs nanoprobe was utilised for the instantaneous detection of As3+ and MBTZ. The limit of detection values were calculated to be 30 nM and 0.44 μM with a good linearity for As3+ and MBTZ, respectively. In addition, a solid sensor has been fabricated to recognize As3+ in wastewater, revealing its potential for on-site application in the near future.

A highly sensitive facile plasmonic scheme for assessment of melamine in raw milk.

This work presents two novel devices with a microcontroller and two different light sensors, namely, Light Dependent Resistor (LDR) and Ambient Light Sensor (ALS), which can provide a quantitative output from the colorimetric variations of citrate capped borohydride reduced silver nanoparticles (AgNPs) and citrate capped gold nanoparticles (AuNPs) upon addition of melamine adulterated milk. The limit of detection (LOD) of the LDR setup with AgNPs and AuNPs was found to be 1.24 ppm and 1.68 ppm, respectively, and the corresponding recovery rates were 92.86% and 88.57%, respectively. The device fabricated with the ALS with AgNPs displayed a recovery rate of 97.14% with a LOD value of 0.64 ppm.

A starch-polyvinyl alcohol polymer film-based on-site sensor for ammonia: a cost effective day-to-day technique for monitoring fish and meat spoilage.

Ammonia or biogenic amines released by protein degradation during food spoilage have various ill effects on human health and the environment. Herein, an economical colorimetric bisphenol-based sensor was developed from inexpensive reagents and a simple synthetic method for detecting ammonia and monitoring food spoilage. The slightest addition of NH3 significantly changed the absorption of BP, which was reflected in the detection limit value for NH3 (7.89 × 10-7 M). The film-based sensor developed by immobilizing BP onto a starch-polyvinyl alcohol (PVA) matrix enabled both the rapid and visual onsite detection of ammonia and the determination of the RGB contents using a digital application. The blue content of the film linearly changed with the extent of the spoilage of fish and meat samples. This linear change enabled the film-based sensor to act as an excellent food quality indicator for hourly food quality monitoring. The aerial reversibility of the film empowered its use for many cycles without the use of any reagents.

Direct SERS Detection of Folic Acid Using Modified Graphene Oxide-Gold Nanobowl Composites.

Gold nanobowls (AuNBs) synthesized by the template-free method were deposited on graphene oxide (GO) to obtain an ultrasensitive surface enhanced Raman spectroscopy (SERS) platform for folic acid (FA) detection. GO was conditioned in aqueous solutions at various pH values to optimize the adsorption of the FA molecule and the intensity of the SERS signal. It was found that the conditioning procedure influences the orientation of FA on the SERS supports and the quality of the spectra in result. The limit of detection (LOD) for FA was equal to 10-12 M for the best combination of GO conditioned at pH = 1 and AuNBs (GO-1/AuNBs). The composites of AuNBs with GO conditioned in solutions of higher pH were less efficient. The LOD values were equal to 10-8 M for AuNBs deposited on GO conditioned at pH = 5.6 (GO-5.6/AuNBs) and 10-7 M for AuNBs deposited on GO conditioned at pH = 13 (GO-13/AuNBs). The high sensitivity of the GO-1/AuNBs composite has been explained by the high adsorption of FA and the molecular orientation with a p-aminobenzoic ring attached to the surface. We suppose that such an orientation fosters efficient charge transfer between the adsorbed molecule and the support, which in turn enhances the SERS intensity by the chemical effect in addition to the electromagnetic enhancement yield by AuNBs. The adsorbed FA molecules attain the random conformation or adsorption through the pteridine ring on the supports with GO conditioned at higher pH. Such orientation results in less efficiency in obtaining the enhancement through the chemical mechanism.

Sensitive Detection of Hg2+ and l-Cysteine through Optical Asymmetry-Tuned Fluorescence Switch Off-On Behavior in N-Doped Chiral Carbon Dot.

Blue-emissive nitrogen-doped chiral carbon dots (d-NCD230 and l-NCD230) exhibiting antipodal chiroptical activity, synthesized from the thermal pyrolysis of citric acid and d/l-aspartic acid in 1:2 molar ratios, have been explored as chirality-based fluorescent turn-off/on probes for the detection of Hg2+ and l-cysteine (l-Cys). Circular dichroism (CD) spectroscopy revealed that the chiroptical activity originates from a synergy among intrinsic chirality, chiral precursors on the NCD surface, and hybridization of lower energy levels within the embedded chiral chromophore. Quantitative analysis of optical asymmetry using the Kuhn asymmetry factor (g) at the CD signal of 312 nm showed a higher value for d-NCD230 (1.03 × 10-4) compared to l-NCD230 (1.13 × 10-5). Moreover, we have demonstrated chirality transfer and chiral inversion phenomena in d/l-NCDs by preparing carbon dots with different precursor ratios at different temperatures and probing them through CD spectroscopy. The NCDs exhibited selective fluorescence quenching in the presence of Hg2+, demonstrating linearity in the Stern-Volmer plot. Limits of detection (LODs) for Hg2+ were calculated to be 129 and 192 nM for d-NCD230 and l-NCD230, respectively, in the 0-150 μM concentration range. The quenching mechanism involves nonradiative electron transfer due to Hg2+ binding to oxygen-rich functional groups on the d/l-NCD230 surface. The slight variation in LOD values between d-NCD230 and l-NCD230 indicates the negligible effect of the chirality on Hg2+ sensing. Notably, the fluorescence intensity of d/l-NCD230 could be restored upon adding l-cysteine, with d-NCD230 showing a more pronounced enhancement than l-NCD230. This differential response is attributed to a preferential stereoselective interaction arising from the homochirality of d-NCD230/Hg2+ and l-cysteine. These findings demonstrate the potential of chiral nitrogen-doped carbon dots as sensitive and selective probes for Hg2+ and l-cysteine, with implications for environmental monitoring and biological sensing applications.

PH‐Directed Capture‐SELEX for Nanomolar Affinity Aptamers for Kanamycin Detection

AbstractKanamycin A is a widely used antibiotic, although it has a narrow therapeutic window demanding highly accurate monitoring. The sensing of kanamycin A using aptamers is of great interest since aptamers can be used for continuous monitoring with a rapid response. While kanamycin has been the target for at least four previous aptamer selections, the binding affinities of the reported DNA aptamers are still sub‐optimal. All the previous aptamer selections were performed at pH 7.5 or higher. Given that kanamycin A has four amino groups with pKa values close to 7, we herein selected DNA aptamers for kanamycin A at both pH 6 and pH 8. The selection at pH 6 enriched aptamers although the pH 8 selection library remained highly diverse in the end. The best aptamer named KAN6‐1 showed a dissociation constant of around 320 nM measured using isothermal titration calorimetry in the selection buffer. In buffers without salt, binding can happen from pH 6 to 8. Specific binding was confirmed using mutation studies. A strand displacement assay was developed with a limit of detection (LOD) of 100 nM in buffer. Similar LOD values were also obtained in lake water and in 10 % human serum. Comparisons were also made with some previously reported DNA aptamers. This study shows the importance of pH value on the selection of aptamers and provides a new aptamer for kanamycin A detection.