μL Sample Volume Research Articles

Simultaneous spectrophotometric determination of the residual of ciprofloxacin, famotidine, and tramadol using magnetic solid phase extraction coupled with multivariate calibration methods

In this work, a sensitive, simple, and inexpensive method have been developed based on magnetic solid Phase extraction for simultaneous spectrophotometric determination of ciprofloxacin (CIP), tramadol (TRA), and famotidine (FA) in the plasma, hospital waste, and river water. For this purpose, Fe3O4/GO-COOH nanocomposite was synthesized and characterized by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The effects of parameters on the extraction efficiency including pH, amount of sorbent, extraction time, elution solvent and its volume, and desorption time were evaluated and optimized.Under the optimal extraction conditions: 50 mg of Fe3O4/GO-COOH nanocomposite, pH 5, extraction time 20 min, 20 mL of sample volume and eluting with 2 mL methanol: ammonium (0.2 M) at 4 min, good linearity for CIP (0.03–1.5 mg L-1), TRA (0.05–3 mg L-1) and FA(0.05–3 mg L-1) was obtained with an acceptable coefficient of determination (R2˃0.99). The absorption UV spectra of these drugs hardly overlap; thus, use of proper calibration methods is useful for their simultaneous spectrophotometric determination. After pre-concentration, partial least squares regression (PLS) as a multivariate calibration technique was utilized for analyzing the UV spectrum (240–320 nm) and simultaneous determination of drugs under the optimum condition. The results of the proposed method showed the low root mean square difference (RMSD) and high correlation coefficient (R2) of the prediction set of mixtures associated with the CIP, TRA, and FA. The developed method was also applied for simultaneous determination of three drugs in the spiked samples of plasma, hospital waste, and river water. The recoveries obtained by PLS lied within the range of 85–101%.

Simultaneous determination of 24,25- and 25,26-dihydroxyvitamin D3 in serum samples with liquid-chromatography mass spectrometry – A useful tool for the assessment of vitamin D metabolism

Vitamin D status is typically assessed by the measurement of 25-hydroxyvitamin D (25(OH)D). However, in selected patient groups the sole determination of 25(OH)D has been proven insufficient for this purpose. The simultaneous measurement of additional vitamin D metabolites may provide useful information for a better evaluation of the vitamin D status. Therefore, we developed and validated a liquid chromatography tandem mass spectrometry (LC-MS/MS) method for the simultaneous determination of 25(OH)D3, 25(OH)D2, 24,25(OH)2D3 and additionally 25,26(OH)2D3, which was identified with a synthesized pure substance.Pure and deuterated substances were used to prepare calibrators and internal standards for all target metabolites. Pre-analytical sample preparation comprised protein precipitation followed by liquid-liquid-extraction and derivatization with 4-Phenyl-1,2,4-triazole-3,5-dione (PTAD) using 50 µL sample volume. Samples were analyzed on an Agilent HPLC 1260 system equipped with a silica-based Kinetex® 5 µm F5 100 Å core-shell column (150 × 4.6 mm) coupled to a Sciex 4500 mass spectrometer.For all four metabolites, limit of detection (LoD) and limit of quantification (LoQ) ranged from 0.3 to 1.5 nmol/L and 1.0 to 3.1 nmol/L, respectively. Recovery varied between 76.1 % and 84.3 %. Intra- and inter-assay imprecision were <8.6 % and <11.5 %, respectively. The analysis of external and internal quality control samples showed good accuracy for 25(OH)D3, 25(OH)D2, 24(R),25(OH)2D3 and 25,26(OH)2D3. Method comparison studies with human samples that were also analyzed with two other LC-MS/MS methods showed close agreement. Finally, the present method has been shown capable of identifying patients with 24-hydroxylase deficiency, which proves its clinical utility.

Rapid and quantitative detection of SARS-CoV-2 specific IgG for convalescent serum evaluation

Convalescent serum with a high abundance of neutralization IgG is a promising therapeutic agent for rescuing COVID-19 patients in the critical stage. Knowing the concentration of SARS-CoV-2 S1-specific IgG is crucial in selecting appropriate convalescent serum donors. Here, we present a portable microfluidic ELISA technology for rapid (15 min), quantitative, and sensitive detection of anti-SARS-CoV-2 S1 IgG in human serum with only 8 μL sample volume. We first identified a humanized monoclonal IgG that has a high binding affinity and a relatively high specificity towards SARS-CoV-2 S1 protein, which can subsequently serve as the calibration standard of anti-SARS-CoV-2 S1 IgG in serological analyses. We then measured the abundance of anti-SARS-CoV-2 S1 IgG in 16 convalescent COVID-19 patients. Due to the availability of the calibration standard and the large dynamic range of our assay, we were able to identify “qualified donors” for convalescent serum therapy with only one fixed dilution factor (200 ×). Finally, we demonstrated that our technology can sensitively detect SARS-CoV-2 antigens (S1 and N proteins) with pg/mL level sensitivities in 40 min. Overall, our technology can greatly facilitate rapid, sensitive, and quantitative analysis of COVID-19 related markers for therapeutic, diagnostic, epidemiologic, and prognostic purposes.

Comparative Study of Electrochemical Biosensors Based on Highly Efficient Mesoporous ZrO2-Ag-G-SiO2 and In2O3-G-SiO2 for Rapid Recognition of E. coli O157:H7.

Here, we reported an innovative and electrochemical biosensor for the rapid detection of Escherichia coliO157:H7. We fabricated the mesoporous ZrO2-Ag-G-SiO2 (ZAGS) and In2O3-G-SiO2 (IGS) sensors, and cyclic voltammetry (CV) was employed to detect the bacteria. The development of these portable sensors addresses the challenges of conventional time-consuming and more expensive laboratory-based analyses. Hence, the biosensors were highly selective to detect E. coli. The sensor could recognize an individual E. coli cell in 1 μL of sample volume within 30 s. E. coli live cells tied down on sample nanoparticles worked toward the definite acquirement of E. coli. The high thickness of negative charge on the surface of E. coli cells effectively regulated the concentration of dominant part charge carriers in the mesoporous channel, allowing a continuous check of E. coli concentration in a known sample. The signal current decreased linearly, while the E. coli concentration increased from 1.0 × 101 to 1.0 × 1010 CFU/mL. ZAGS and IGS biosensors could detect E. coli in the range from 101 to 1010 CFU/mL. ZAGS and IGS biosensors in this investigation showed great specificity, reproducibility, stability, and selectivity and are expected to have a great impact on applications in the detection of foodborne pathogens.

Development of HiBiT-Tagged Recombinant Infectious Bronchitis Coronavirus for Efficient in vitro and in vivo Viral Quantification.

Coronaviruses (CoVs) are enveloped (+) ssRNA viruses of veterinary and medical importance. Because recombinant CoVs with reporter proteins fused with viral proteins are usually non-viable or unstable, a small and quantifiable epitope tag would be beneficial to CoV research. In this study, we integrated the NanoLuc Binary Technology to the reverse genetics of infectious bronchitis virus (IBV), a prototypic gammacoronavirus. The 11-amino-acid HiBiT tag was inserted to the spike (S) or membrane (M) protein, and the recombinant IBVs (rS-HiBiT and rM-HiBiT) were characterized. Compared with the rIBV-p65 control, rS-HiBiT exhibited comparable growth kinetics, whereas rM-HiBiT replicated slightly slower. The levels of HiBiT-tagged S and M proteins in the infected cells or the culture supernatant could be both rapidly (~15 min) and efficiently (30 μL sample volume) determined using the HiBiT luminescence assay. Notably, replication of the HiBiT-tagged IBV could be monitored continuously in an infected chicken embryo, and rS-HiBiT was genetically stable for at least 20 passages. By integrating the HiBiT tagging system with CoV reverse genetics, this new reporter system may facilitate future study of CoV replication and pathogenesis.

Microfluidic Electrochemical Sensor for Cerebrospinal Fluid and Blood Dopamine Detection in a Mouse Model of Parkinson's Disease.

Parkinson's disease (PD) is a progressive neurodegenerative disorder involving dopaminergic neurons from the substantia nigra. The loss of dopaminergic neurons results in decreased dopamine (DA) release in the striatum and thus impaired motor functions. DA is one of the key neurotransmitters monitored for the diagnosis and during the progression and treatment of PD. Therefore, sensitive and selective DA detection methods are of high clinical relevance. In this study, a new microfluidic device utilized for electrochemical DA detection is reported. The microfluidic sensing device operates in the range of 0.1-1000 nM DA requiring only ∼2.4 μL sample volume, which corresponds to detectable 240 amol of DA. Using this sensor, we were able to monitor the changes in DA levels in cerebrospinal fluid and plasma of a mouse model of PD and following the treatment of drug l-3,4-dihydroxyphenylalanine.

Development of a novel electrochemical immuno-biosensor for circulating biomarkers of the inner ear

Current approaches for diagnosis of hearing or vestibular disorders are mostly based on physical examinations that cannot provide information about the exact location of cellular damage inside the inner ear. Therefore, there is a need for new diagnostic methods capable of identifying the sites of damage through the detection of inner ear blood-circulating biomarkers. Here, we developed the first biosensor platform for rapid detection of otolin-1 and prestin, blood-circulating proteins specifically expressed in the vestibule and cochlea, respectively. The platform was designed on a DNA-based immunoassay that employed conjugated antibodies for target protein recognition, which when bound, altered the DNA-DNA hybridization on the surface, resulting in generation of a concentration-dependent signal. The signal was recorded when the redox moiety brought to the surface by the target enabled a selective electrochemical output directly in whole blood. Signal amplification was acquired by employing high-curvature nanostructured electrodes for sensitive sample analysis at picomolar concentrations with a three-fold quantitative range. The combination of nanostructuring and optimum density of the probes on the surface provided low-picomolar detection limits while utilizing small 10 μL sample volume with a 10-min response time. The proposed immuno-biosensor is highly selective and quantitative and can easily be adapted for rapid detection of any blood-circulating protein using their specific antibodies as recognition elements.

Magnetic Beads for Desalting of Monoclonal Antibodies and Antibody-Drug Conjugates.

Characterization of antibody-drug conjugates (ADCs) using mass spectrometry (MS) is important in drug discovery and formulation development and as part of the quality control processes. To facilitate electrospray ionization (ESI) and produce high-quality mass spectra, common components of storage solutions for monoclonal antibodies (mAbs) and ADCs, such as nonvolatile phosphate-buffered saline (PBS), should be replaced before analysis. Centrifugal spin-type kits are extensively used for the desalting or buffer-exchange of mAbs and ADCs samples. The commercially available kits commonly require at least 100 μL of a sample at 1 mg/mL for optimal recovery. However, most ESI-MS based analyses require no more than 25 μg of protein for triplicate injection. In this study, we present a novel method for desalting of ADCs and mAbs building on the SP3 approach with nonfunctionalized carboxylate coated magnetic beads without affinity ligands. The analytes bind to the hydrophilic beads upon the addition of organic solvent, and various solutions of volatile salts or acids can be used in the elution step. The optimized protocol allowed for 88% recovery of ADC at a 25 μL sample volume and 90% recovery at 100 μL. More than 90% of the salts were removed using a process of 20 min. The intra- and interday precision showed little variation with an RSD of 1% and 2%, respectively. The compatibility of this new workflow with low sample volumes is highly valuable since a smaller fraction of the sample is wasted for analysis of the expensive analytes, without compromising recovery.

Dispersive solid-phase microextraction with arginine-functionalized magnetic nanocomposite as the sorbent for separation and preconcentration of aspartame and optimization using response surface methodology

In this study, the surface of magnetic dialdehyde starch nanocomposite has been modified with arginine amino acid (Arg) and employed as an adsorbent for the enrichment of aspartame (ASP) in different real samples. Magnetite dispersive solid-phase microextraction (MDSPME), which had been combined with spectrophotometry, has been used to determine the extracted aspartame. The Plackett–Burman design has been employed to investigate the influence of main parameters including the amount of salt, sample volume, amount of sorbent, dispersive solution volume, desorption, and extraction time, and central composite design has been used to obtain the optimum condition in MDSPME method. Under optimum conditions, 15 ml of sample volume, 1.5 ml of ethanol as dispersive solvent, 10 min of extraction time, 15 min of desorption time, 10 mg of sorbent, and 0 w/v % of salt, the calibration graph has been observed to be linear in a concentration range of 2–15 µg ml−1, while the limit of detection has been 0.064 µg ml−1. The relative standard deviations of 3.64 and 4.12 have been obtained at 8 µg ml−1 level of aspartame for the intra- and inter-day analysis. In addition, the enrichment factor has been about 128. This procedure has been successfully utilized for distinguishing the existing aspartame in two kinds of beverage that had been procured from local markets and drinkable water.

Determination of polycyclic aromatic hydrocarbons in non-alcoholic beer by mechanical stir bar sorptive extraction-gas chromatography.

A polyacrylonitrile (PAN)/polydimethylsiloxane (PDMS) coating was electrospun on the shaft of the mechanical stir bar sorptive extraction (MSBSE) setup. MSBSE equipped with the PAN/PDMS coating and coupled with gas chromatography/flame ionization detector (MSBSE-PAN/PDMS-GC/FID) was used to determine some polycyclic aromatic hydrocarbons (PAHs) in non-alcoholic beer samples. The effective parameters including extraction time, desorption time, stirring speed and sample volume were optimized by the response surface methodology (RSM) based on the central composite design (CCD). The optimum condition was obtained in 60 min of extraction time, 10 min of desorption time, 1300 rpm of stirring speed and 16 mL of sample volume. The calibration curves of PAHs were linear in the range 5–1000 ng mL−1. The limit of detections (LODs) was in the range of 0.009–0.5 ng mL−1 and the limit of qualifications (LOQs) was varied between 0.03 and 1.5 ng mL−1. The relative recoveries and enrichment factors were in the range of 94–98% and 117–126, respectively, and the relative standard deviations (RSDs) were below 11.4%.Graphic abstract

Adsorption Studies of Methylene Blue by Encapsulated Nano-Carbonaceous Alginate Beads

Two different nano-carbonaceous materials namely, multi-walled carbon nanotubes and graphene oxide were encapsulated with biopolymer alginate and employed as adsorbents for the removal of methylene blue dye from aqueous solution. To evaluate the performance of synthesized adsorbents, several parameters including adsorbent dosage, sample volume, stirring speed, sample pH, contact time and initial dye concentration were optimized. The optimum conditions were found as follow: 0.1g adsorbent dosage, 400 rpm stirring speed, 10 mL of sample volume, 180 minutes contact time, pH 11 and 20 mg/L initial concentration of methylene blue. From the results, the encapsulated Alginate-carbonaceous beads gave higher removal percentage as compared to pristine alginate beads. This could attribute by additional hydrophobic and π-π interaction contributed from aromatic rings of carbonaceous material towards methylene blue molecular structure. Whilst, kinetic studies showed that the adsorption process accurately represented by a pseudo second-order model.

A Micromethod for Polyphenol High-Throughput Screening Saves 90 Percent Reagents and Sample Volume.

There is ample evidence that polyphenols are important natural substances with pronounced antioxidative properties. This study aimed to develop a fast and reliable method to determine total polyphenol content (TPC) in foodstuffs and human samples. The microtitration format offers the advantage of low sample volumes in the microlitre range, facilitating high-throughput screening with 40 samples simultaneously. We accordingly adjusted the so-called Folin–Ciocalteu method to a microtitre format (polyphenols microtitre—PPm) with 90% reduction of reagents. The assay was standardized with gallic acid in the range between 0.1 and 3 mM, using a 20 µL sample volume. The intra-assay coefficient of variation (CV) was less than 5%, and inter-assay CV was in the range of 10%. Wavelength was measured at 766 nm after two hours of incubation. This micromethod correlates significantly with both the classical Folin–Ciocalteu method and High-Performance Thin-Layer Chromatography (HPTLC) (r2 = 0.9829). We further observed a significant correlation between PPm and total antioxidants (r2 = 0.918). The highest polyphenol concentrations were obtained for red, blue, and black fruits, vegetables, and juices. Extracts of red grapes could be harvested almost sugar free and might serve as a basis for polyphenol supplementation. Beer, flour, and bread contained polyphenol concentrations sufficient to meet the minimal daily requirement. We conclude that PPm is a sensitive and reliable method that detects polyphenols even in samples diluted 10-fold. The literature strongly recommends further investigations on the effects of polyphenol uptake on human and animal health.

Development of a Rapid Method for Determination of Main Higher Alcohols in Fermented Alcoholic Beverages Based on Dispersive Liquid-Liquid Microextraction and Gas Chromatography-Mass Spectrometry

Higher alcohols are important flavor compounds in alcoholic beverages. A new method was developed to determinate the main higher alcohols based on dispersive liquid-liquid microextraction (DLLME) coupled with GC/MS. Huangjiu was selected as an example to develop the method. The optimal DLLME parameters were acquired: the sample was diluted one time with water, no pH adjustment was required, 600 μL dichloromethane as extraction solvent, 1.5 mL acetonitrile as dispersant, 3.5 mL of sample volume, 1 min of extraction time and no salt addition. The performance of the method was satisfactory. The results obtained from DLLME were consistent with those from head space solid phase microextration (HS-SPME) and static headspace (SHS). In addition, DLLME is simpler and more time-saving compared with HS-SPME and SHS. These results indicated that the present method is satisfactory and suitable for determination of higher alcohols in Huangjiu, especially for routine inspection and batch analysis.

Flow Injection–Indirect Spectrophotometry for Hydroquinone Analysis Based on the Formation of Iron(II)-Phenanthroline Complex

Hydroquinone is an organic antioxidant widely used for skin lightening products which can cause negative impact in excessive use. This study is focused on the development of fast method for the determination of hydroquinone using flow injection-indirect spectrophotometry based on the formation of red complex iron(II)-phenanthroline. In this method, hydroquinone reduced iron(III) to iron(II) which in the presence of phenanthroline formed iron(II)-phenanthroline complex detected at maximum wavelength of 510 nm. The common operational and chemical conditions were optimized and the effect of several interfering compounds was also studied to achieve the highest sensitivity with acceptable analysis time. The optimum method performance was obtained under the conditions of 100 µL sample volume, 50 cm mixing coil-1and 75 cm mixing coil-2, 5 ml/min flow rate, 100 mgL-1 Iron(III) concentration, and 0.15 % phenanthroline. Under these conditions the proposed FI-spectrophotometry gave results to linear calibration over the concentration range from 2-100 mgL-1 (y = 0.028x and R2 of 0.999). The method was not interfered in the presence of vitamin C 1 mgL-1 and resorcinol up to 10 mgL-1. However, the higher concentration of vitamin C ≥10 ppm and resorcinol ≥ 20 ppm gave significant error of measurements. Method validation using standard additions gave results to average recovery value of 97.02 %, which indicates that the FI-spectrophotometry method can be used as an alternative method for determining hydroquinone in cosmetic.

Magnetic solid-phase extraction based onCoriolus versicolor-immobilized-Fe2O3nanoparticles for preconcentration and determination of Al(III) in waterand food samples

A method for preconcentration of Al(III) prior to its determination by inductively coupled plasma-optical emission spectrometry (ICP-OES) was developed because the sensitivity of ICP-OES is insufficient for trace-level measurement of Al(III). The method is based on the use of Coriolus versicolor}-immobilized $\gamma $-Fe$_{2}$O$_{3}$ magnetic nanoparticles as a solid phase sorbent. The best experimental conditions were found as pH 6.0, 2.0 mL/min flow rate, 100 mg amount of C. versicoloron 150 mg of $\gamma $-Fe$_{2}$O$_{3}$ nanoparticles, and 500 mL of sample volume. The Al(III) absorbed on biosorbent was eluted with 5.0 mL of 1.0 mol/L HCl. Limit of detection, limit of quantitation, linear range, correlation coefficient, relative standard deviation, and preconcentration factor were achieved as 0.03 ng/mL, 0.11 ng/mL, 0.2 to 20 ng/mL, 0.9994, 3%, and 100, respectively. Al(III) was preconcentrated in different water and food samples after successful results were achieved in the case of certified reference samples.

Diazonium-Modified Screen-Printed Electrodes for Immunosensing Growth Hormone in Blood Samples

Altered growth hormone (GH) levels represent a major global health challenge that would benefit from advances in screening methods that are rapid and low cost. Here, we present a miniaturized immunosensor using disposable screen-printed carbon electrodes (SPCEs) for the detection of GH with high sensitivity. The diazonium-based linker layer was electrochemically deposited onto SPCE surfaces, and subsequently activated using covalent agents to immobilize monoclonal anti-GH antibodies as the sensing layer. The surface modifications were monitored using contact angle measurements and X-ray photoelectron spectroscopy (XPS). The dissociation constant, Kd, of the anti-GH antibodies was also determined as 1.44 (±0.15) using surface plasmon resonance (SPR). The immunosensor was able to detect GH in the picomolar range using a 20 µL sample volume in connection with electrochemical impedance spectroscopy (EIS). The selectivity of the SPCE-based immunosensors was also challenged with whole blood and serum samples collected at various development stages of rats, demonstrating the potential applicability for detection in biological samples. Our results demonstrated that SPCEs provided the development of low-cost and single-use electrochemical immunosensors in comparison with glassy carbon electrode (GCE)-based ones.

Perspectives on microwave coupling into cylindrical and spherical rotors with dielectric lenses for magic angle spinning dynamic nuclear polarization.

Continuous wave dynamic nuclear polarization (DNP) increases the sensitivity of NMR, yet intense microwave fields are required to transition magic angle spinning (MAS) DNP to the time domain. Here we describe and analyze Teflon lenses for cylindrical and spherical MAS rotors that focus microwave power and increase the electron Rabi frequency, ν1s. Using a commercial simulation package, we solve the Maxwell equations and determine the propagation and focusing of millimeter waves (198 GHz). We then calculate the microwave intensity in a time-independent fashion to compute the ν1s. With a nominal microwave power input of 5 W, the average ν1s is 0.38 MHz within a 22 μL sample volume in a 3.2 mm outer diameter (OD) cylindrical rotor without a Teflon lens. Decreasing the sample volume to 3 μL and focusing the microwave beam with a Teflon lens increases the ν1s to 1.5 MHz. Microwave polarization and intensity perturbations associated with diffraction through the radiofrequency coil, losses from penetration through the rotor wall, and mechanical limitations of the separation between the lens and sample are significant challenges to improving microwave coupling in MAS DNP instrumentation. To overcome these issues, we introduce a novel focusing strategy using dielectric microwave lenses installed within spinning rotors. One such 9.5 mm OD cylindrical rotor assembly implements a Teflon focusing lens to increase the ν1s to 2.7 MHz within a 2 μL sample. Further, to access high spinning frequencies while also increasing ν1s, we analyze microwave coupling into MAS spheres. For 9.5 mm OD spherical rotors, we compute a ν1s of 0.36 MHz within a sample volume of 161 μL, and 2.5 MHz within a 3 μL sample placed at the focal point of a novel double lens insert. We conclude with an analysis and discussion of sub-millimeter diamond spherical rotors for time domain DNP at spinning frequencies >100 kHz. Sub-millimeter spherical rotors better overlap a tightly focused microwave beam, resulting in a ν1s of 2.2 MHz. Lastly, we propose that sub-millimeter dielectric spherical microwave resonators will provide a means to substantially improve electron spin control in the future.

A novel microneedle device for controlled and reliable liquid biopsy of the human inner ear

Sensorineural hearing loss is the most common sensory deficit worldwide, yet our understanding of the underlying pathophysiology is limited by the challenges of access to the inner ear in a safe and reliable manner. We present a novel microneedle device for trans-round window membrane liquid biopsy, which utilizes controlled depth of perforation and microliter aspiration control to safely biopsy fluids of the inner ear. Of eleven devices tested in fresh frozen human temporal bones, seven demonstrated alignment between electrical, visual and tactile detection of round window membrane perforation, and nine were successful in aspiration of meaningful diagnostic samples from the perilymphatic space. Purity of the average perilymph sample was 69% for a 5 μL sample volume, equivalent to 3.5 μL attributable to perilymph. Diagnostic success was shown both by transmastoid facial recess and transcanal tympanotomy approach. This device can enable new advances in the understanding of inner ear pathology, and brings us one step closer to liquid biopsy of the inner ear becoming a routine part of clinical care.

Thiocyanate Determination using Technique of Flow Injection-Gas Diffusion Spectrophotometry with Cerium (IV)-Ninhydrin Reagent.

Numerous food plants contain thiocyanate, which can inhibit iodine uptake of thyroid gland and induce to the risk of iodine deficiency disorders (IDD). This research is focused on the development of new method for thiocyanate determination based on the formation of red hydrindantin using spectrophotometric flow injection (FI)–gas diffusion technique. In this technique, thiocyanate is oxidized by cerium (IV) in the acid donor stream to form hydrogen cyanide which diffuses through the membrane in the gas diffusion cell and reacts selectively with alkaline ninhydrin in the acceptor stream to form a red hydrindantin detected by spectrophotometer at 485 nm. The common operational conditions including sample volume, the length of mixing coil, and the flow rate as well as chemical parameters (concentration of cerium (IV) and ninhydrin, and pH reaction) were optimized with respect to sensitivity, analysis time, and linearity. The optimum condition notified by highest absorbance with sharp single peak and fast analysis was obtained under flow rate of 2 mL min−1, 300 µL sample volume, 75 cm mixing coil, 0.01 M cerium (IV), 1 % ninhydrin, and pH of 11. The interfering ions frequently exist with thiocyanate were also studied. Under the optimized conditions, the method showed linear for thiocyanate concentration from 5-30 mgL−1 and sampling rate of 120 s/h with a satisfactory reproducibility (RSD < 2% at n=3). This method has been successfully applied to determine thiocyanate in saliva from smoker and non-smoker and the results showed good agreement with those obtained from standard spectrophotometry method.

Disposable Biosensor Based on Amidase/CeO2/GNR Modified Inkjet‐printed CNT Electrodes‐droplet Based Paracetamol Detection in Biological Fluids for “Point‐of‐care” Applications

AbstractA disposable acetaminophen biosensor based on inkjet‐printed CNT electrodes (IJPCNT) modified with amidase/cerium dioxide@graphene nanoribbons composite was developed (ACeO2@GNR/IJPCNT). The enzyme amidase A was used for the first time as a recognition element. Inkjet‐printed CNT electrodes served as a basis for the construction of a biosensor that enables droplet detection using 5 μL sample volume. The biosensor showed high selectivity, sensitivity, a low detection limit of 0.18 μM and a wide working linear range from 1 to 100 μM. The proposed approach allows fast and reliable detection of acetaminophen in biological fluids with negligible matrix effect and remarkable reproducibility.