Preparation and application of multiple particle binding-liposomes for electrochemiluminescent signal amplification in bioassays.

In this study, multiple particle binding-liposomes (MPB-Lips), encapsulating the luminophore tris(2',2-bipyridyl)ruthenium (II) complex ([Ru(bpy)3]2+), were developed as an electrochemiluminescence (ECL) signal amplifier and were applied to detect the model analyte streptavidin (SA) using the indirect competitive ECL method. The MPB-Lips were prepared by mixing various ratios of two different liposomes-one containing a phospholipid with a primary amine group and a biotinyl group (BIO/NH2-Lip) and one containing a phospholipid with an N-hydroxysuccinimide group (NHS-Lip) to allow binding between particles via amide bonds. Quartz crystal microbalance analysis using SA-modified gold-coated quartz crystals showed that the frequency shift values of MPB-Lips gradually decreased in the order BIO/NH2-Lip:NHS-Lip = 1:0 < 1:1 < 1:3 < 1:5. This indicated that MPB-Lips were successfully formed. The indirect competitive ECL method using SA-modified gold electrodes showed that the 1:5-Lip system had greater sensitivity than the 1:0-Lip system-the limit of detection and quantification values for the systems were 1.84 and 6.30 µg mL-1 for 1:0-Lip, and 1.20 and 1.74 µg mL-1 for 1:5-Lip. Finally, the recovery of SA spiked in fetal bovine serum samples using the 1:5-Lip system showed good accuracy and precision with a recovery rate of 83-106% and relative standard deviation of 4-14%. Our study demonstrated that the MPB-Lips system was an effective and useful ECL amplifier and the ECL method using MPB-Lips could be applied to detect an analyte in a real sample.

A serum protein signature at the time of Uveal Melanoma diagnosis predicts long-term patient survival.

PURPOSE: To develop a prognostic test based on a single blood sample obtained at the time of uveal melanoma diagnosis. METHODS: 83 patients diagnosed with posterior uveal melanoma between 1996 and 2000 were included. Peripheral serum samples were obtained at diagnosis and kept at -80 °C until this analysis. Protein profiling of 84 cancer-related proteins was used to screen for potential biomarkers and a prognostic test that stratifies patients into metastatic risk categories was developed (serUM-Px) in a training cohort and then tested in a validation cohort. RESULTS: Low serum leptin levels and high osteopontin levels were found to identify patients with poor prognosis and were therefore selected for inclusion in the final test. In the validation cohort, patient sex and American Joint Committee on Cancer stages were similarly distributed between the low, intermediate, and high metastatic risk categories. With increasing metastatic risk category, patients had shorter metastasis-free- and overall survival, as well as greater cumulative incidence of uveal melanoma-related mortality in competing risk analysis (P = 0.007, 0.018 and 0.029, respectively). In multivariate Cox regression, serUM-Px was an independent predictor of metastasis with tumor size and patient sex as covariates (hazard ratio 3.2, 95% CI 1.5-6.9). CONCLUSIONS: A prognostic test based on a single peripheral venous blood sample at the time of uveal melanoma diagnosis stratifies patients into low, intermediate, and high metastatic risk categories. Prospective validation will facilitate its clinical utility.

Label-free colorimetric sensor for Pb2+ determination using catalytic activity of MnO2 nanoflowers and elongated aptamer.

In this study, a label-free aptasensor utilizing colorimetric properties was developed to detect Pb2+ with high sensitivity. The approach involved applying modified aptamer which enhanced the oxidase-mimicking activity of MnO2 nanoflowers. This innovative method provides an efficient means for monitoring Pb2+ ions without requiring any labeling techniques. The fundamental principle of this aptasensor is based on the adsorption of a modified aptamer onto MnO2 nanoflowers' surface, which in turn increases their affinity for chromogenic substrates and enhances their catalytic activity. The proposed aptasensor exploits the high sensitivity due to the extension of the aptamer sequence length by terminal deoxynucleotidyl transferase (TdT). Under optimum experimental conditions, the developed colorimetric aptasensor indicated a linear detection range from 4 to 80 nM with a limit of detection (LOD) of 1.4 nM. Moreover, the aptasensor successfully monitored Pb2+ in the drinking water, milk and human serum samples. Henceforth, the colorimetric aptasensor exhibited in this study possesses several benefits such as uncomplicated operation, cost-effectiveness, label-free detection and remarkable sensitivity. Thus rendering it a suitable option for analyzing intricate samples.

A Selective Fluorescent Nanoprobe Based on Graphene Quantum Dots and Hg2+ for the Determination of Tetracycline in Biological Samples.

A simple, sensitive, and selective fluorometric method based on graphene quantum dots and Hg2+ is presented for the determination of tetracycline. The fluorescence emission of graphene quantum dots at 463 nm decreased in the presence of Hg2+ ions due to its electrostatic interaction with the negatively charged surface of quantum dots at pH = 8.0. The addition of tetracycline to this system resulted in the retrieval of the fluorescence emission of the graphene quantum dots proportional to the tetracycline concentration. This is because of the interaction between tetracycline and Hg2+ that results in the release of the quantum dots' surface. Under the optimized conditions, the calibration curve indicated good linearity in the range of 2.0-44.0 nmol L-1 with a detection limit of 0.52 nmol L-1 for tetracycline. The designed nanoprobe was capable of the determination of tetracycline in serum and urine samples.

Facile immobilization of cholesterol oxidase on Pt,Ru-C nanocomposite and ionic liquid-modified carbon paste electrode for an efficient amperometric free cholesterol biosensing.

In present work, the enzyme cholesterol oxidase (ChOx) was immobilized by Nafion® (Naf) on Pt,Ru-C nanocomposite and an ionic liquid (IL)-modified carbon paste electrode (CPE) in order to create cholesterol biosensor (Naf/ChOx/Pt,Ru-C/IL-CPE). The prepared working electrodes were characterized using scanning electron microscopy-energy-dispersive spectrometry, while their electrochemical performance was evaluated using electrochemical impedance spectroscopic, cyclic voltammetric, and amperometric techniques. Excellent synergism between IL 1-allyl-3-methylimidazolium dicyanamide ([AMIM][DCA]), Pt,Ru-C, and ChOx, as modifiers of CPE, offers the most pronounced analytical performance for improved cholesterol amperometric determination in phosphate buffer solution pH 7.50 at a working potential of 0.60 V. Under optimized experimental conditions, a linear relationship between oxidation current and cholesterol concentration was found for the range from 0.31 to 2.46 µM, with an estimated detection limit of 0.13 µM and relative standard deviation (RSD) below 5.5%. The optimized amperometric method in combination with the developed Naf/ChOx/Pt,Ru-C/IL-CPE biosensor showed good repeatability and high selectivity towards cholesterol biosensing. The proposed biosensor was successfully applied to determine free cholesterol in a human blood serum sample via its enzymatic reaction product hydrogen peroxide despite the presence of possible interferences. The percentage recovery ranged from 99.08 to 102.81%, while RSD was below 2.0% for the unspiked as well as the spiked human blood serum sample. The obtained results indicated excellent accuracy and precision of the method, concluding that the developed biosensor can be a promising alternative to existing commercial cholesterol tests used in medical practice.

One-step fabrication of COF-coated melamine sponge for in-syringe solid-phase extraction of active ingredients from traditional Chinese medicine in serum samples.

In this study, a covalent organic framework (COF)-TpBD-supported melamine sponge (MS) was fabricated through a one-step hydrothermal method. The obtained monolithic column was then applied in in-syringe solid-phase extraction (IS-SPE) for the separation of three volatile ingredients from serum samples. Given credit for the superior adsorption capacity of the COF and the homogeneous microporous property of MS, the developed column exhibited satisfactory separation of the targets. And the dominating adsorption mechanism was the hydrophobic interaction forces between TpBD and targets and the high mass transfer efficiency provided by the large pore structure of MS. The results of dynamic adsorption showed that the MS@TpBD column displayed much better adsorption performance than blank MS and TpBD. And it has featured great reusability up to 5 cycles and obtained satisfied recovery values (87.9 ~ 110.3%) in serum samples. As a result of sample clean-up, this column offers low limit of detections (LODs) down to 0.014, 0.010, and 0.020 µg/mL, respectively. In summary, we believe that this convenient separation column has prominent application promise in the fields of separating activity ingredients in biological samples.

Silver Nanoparticle-Functionalised Nitrogen-Doped Carbon Quantum Dots for the Highly Efficient Determination of Uric Acid.

The fabrication of efficient fluorescent probes that possess an excellent sensitivity and selectivity for uric acid is highly desirable and challenging. In this study, composites of silver nanoparticles (AgNPs) wrapped with nitrogen-doped carbon quantum dots (N-CQDs) were synthesised utilising N-CQDs as the reducing and stabilising agents in a single reaction with AgNO3. The morphology and structure, absorption properties, functional groups, and fluorescence properties were characterised by transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, ultraviolet spectroscopy, fluorescence spectroscopy, and X-ray diffraction spectroscopy. In addition, we developed a novel method based on AgNPs/N-CQDs for the detection of uric acid using the enzymatic reaction of uric acid oxidase. The fluorescence enhancement of the AgNPs/N-CQDs composite was linear (R2 = 0.9971) in the range of 2.0-60 µmol/L, and gave a detection limit of 0.53 µmol/L. Trace uric acid was successfully determined in real serum samples from the serum of 10 healthy candidates and 10 gout patients, and the results were consistent with those recorded by Qianxinan Prefecture People's Hospital. These results indicate that the developed AgNP/N-CQD system can provide a universal platform for detecting the multispecies ratio fluorescence of H2O2 generation in other biological systems.

Reducing the effects of control materials based on interchangeability of estimates of day-to-day imprecision between commercial control materials and serum samples.

BACKGROUND: Reduce the effects in the storage-and-thawing process of commercial control materials based on their interchangeability evaluation. METHODS: Seven assays-anti-streptolysin O, complement 3, carcinoembryonic antigen, urea, ferritin, total bilirubin, and glucose-were selected. Commercial control materials and serum samples with similar concentrations were chosen as samples. The experiment was carried out in three stages. In the first stage, the assays with statistical differences in imprecision were screened. In the second stage, two specimens were sealed with parafilm and frozen at -80°C and thawed in the water bath, and the imprecision differences were compared again. Finally, the effective means to reduce the effects were included in the standard operating procedure to repeat confirmation. RESULTS: In the first stage, there was only a statistical difference (p < 0.05) in the imprecision of glucose and total bilirubin between two specimens, and the imprecision of control materials was higher than the serum samples. In the second stage, glucose imprecision was not statistically different (p > 0.05) and lower than in the first stage. In the third stage, the methods from the second stage were confirmed to be effective at reducing control material effects. CONCLUSION: Finding variation factors and confirming and standardizing the measures will help lessen commercial control material effects.

Perylene diimide/MXene-modified graphitic pencil electrode-based electrochemical sensor for dopamine detection.

The synthesis of novel architecture comprising perylene diimide (PDI)-MXene (Ti3C2TX)-integrated graphitic pencil electrode for electrochemical detection of dopamine (DA) is reported. The good electron passage between PDI-MXene resulted in an unprecedented nano-adduct bearing enhanced electrocatalytic activity with low-energy electronic transitions. The anionic groups of PDI corroborated enhanced active surface area for selective binding and robust oxidation of DA, thereby decreasing the applied potential. Meanwhile, the MXene layers acted as functional conducive support for PDI absorption via strong H-bonding. The considerable conductivity of MXene enhanced electron transportation thus increasing the sensitivity of sensing interface. The inclusively engineered nano-adduct resulted in robust DA oxidation with ultra-sensitivity (38.1 µAµM-1cm-2), and low detection limit (240 nM) at very low oxidation potential (-0.135 V). Moreover, it selectively signaled DA in the presence of physiological interferents with wide linearity (100-1000 µM). The developed transducing interface performed well in human serum samples with RSD (0.1 to 0.4%) and recovery (98.6 to 100.2%) corroborating the viability of the practical implementation of this integrated system. Graphical abstract Schematic illustration of the oxidative process involved on constructed sensing interface for the development of a non-enzymatic dopamine sensor.

Carbon cloth-based immunosensor for detection of 25-hydroxy vitamin D3.

Vitamin D (VD) deficiency is a global health concern due to its serious health impacts, and at present, the monitoring of VD status is expensive. Here, a novel immunosensor for sensitive and label-free detection of 25-hydroxy vitamin D3 (25VD3) is reported. Nanostructured cerium(IV) oxide (nCeO2) was anchored onto carbon cloth (CC) via electrophoretic deposition to fabricate a nanoplatform (nCeO2/CC). Subsequently, bioactive molecules (anti-25VD3 and BSA) were introduced to fabricate the nanobioplatform BSA/anti-25VD3/nCeO2/CC as an immunosensor. The analytical performance of the developed immunosensor was studied towards 25VD3 detection. The immunosensor provides a broad linear range of 1-200 ng mL-1, high sensitivity of 2.08 µA ng-1 mL cm-2, a detection limit of 4.63 ng mL-1, and a response time of 15 min, which is better than that of previous reports. The biosensor exhibited high selectivity, good reproducibility, and excellent stability for about 45 days. The potential application of the proposed immunosensor was observed for real serum samples towards 25VD3 detection that demonstrated a high correlation with the conventional enzyme-linked immunosorbent assay. Graphical abstract.

SERS-ELISA determination of human carboxylesterase 1 using metal-organic framework doped with gold nanoparticles as SERS substrate.

By in situ synthesis of gold nanoparticles (AuNPs) within the acid-etched (AE) MIL-101 (Cr) framework, AE-MIL-101 (Cr) nanocomposites embedded with AuNPs (AuNP/AE-MIL-101 (Cr)) were prepared as surface-enhanced Raman scattering (SERS) substrate. AuNPs are uniformly distributed and stabilized inside the metal-organic framework (MOF), thus forming more SERS hotspots. The SERS performance of AuNP/AE-MIL-101 (Cr) was evaluated using 4-mercaptophenylboronic acid (4-MPBA), 4-mercaptobenzoic acid (4-MBA), benzidine, and rhodamine 6G (R6G). The SERS substrate displays satisfying stability with very low background signal. When benzidine is used as the Raman reporter, the limit of detection (LOD) can reach 6.7 × 10-13 mol·L-1, and the relative standard deviation (RSD) of the intra- and inter-batch repetitive tests is less than 5.2%. On this basis, we developed a method for the detection of human carboxylesterase 1 (hCE 1) in human serum using AuNP/AE-MIL-101 (Cr) nanocomposite as SERS substrate and enzyme-linked immunosorbent assay (ELISA) colorimetric substrate as SERS marker. This method was used to determine hCE 1 in clinical serum samples without complicated sample pretreatment, and the detection results were consistent with the data determined by ELISA. In the concentration range 0.1-120 ng·mL-1, the SERS signal intensity of benzidine at 1609 cm-1 gradually decreases with the increase of hCE 1 concentration (R2 = 0.9948). The average recoveries of hCE 1 in human serum are in the range 84 to 108%, with RSDs lower than 7.7%. By using AuNP/acid etching-MIL-101(Cr) metal organic framework (MOF) as SERS substrate and enzyme-linked immunosorbent assay (ELISA) colorimetric substrate as the SERS marker, a rapid and sensitive method for the determination of human carboxylesterase 1 (hCE1) in human serum samples has been developed.

Enhancement in MS-based peptide detection by microfluidic free-flow zone electrophoresis.

Matrix components are known to significantly alter the ionization of a target analyte in ESI-based measurements particularly when working with complex biological samples. This issue however may be alleviated by extracting the analyte of interest from the original sample into a relatively simple matrix compatible with ESI mass-spectrometric analysis. In this article, we report a microfluidic device that enables such extraction of small peptide molecules into an ESI-compatible solvent stream significantly improving both the sensitivity and reproducibility of the measurements. The reported device realizes this analyte extraction capability based on the free-flow zone electrophoretic fractionation process using a set of internal electrodes placed across the width of the analysis channel. Employing lateral electric fields and separation distances of 75 V/cm and 600 µm, respectively, efficient extraction of the model peptide human angiotensin II was demonstrated allowing a reduction in its detection limit by one to three orders of magnitude using the ESI-MS method. The noted result was obtained in our experiments both for a relatively simple specimen comprising DNA strands and angiotensin II as well as for human serum samples spiked with the same model peptide.

Signal multi-amplified electrochemical biosensor for voltammetric determination of tau-441 protein in biological samples using carbon nanomaterials and gold nanoparticles to hint dementia.

A signal multi-amplified electrochemical biosensor was fabricated for tau-441 protein, a dementia biomarker. It utilizes a carbon nanocomposite film modified gold electrode. The carbon nanocomposite film was composed of multi-walled carbon nanotubes (MWCNTs), reduced graphene oxide (rGO), and chitosan (CS). For the nanocomposite film, rGO improved the dispersibility of MWCNTs, and the effective surface area of MWCNTs was increased. On the other hand, MWCNTs also increased the interlayer spacing of rGO, resulting in a thinner rGO layer. MWCNTs-rGO had a better conductivity than that of MWCNTs and rGO due to the synergy effect. Biocompatible CS was employed for immobilization of the specific antibody. Tau-441 protein was modified with gold nanoparticles (AuNPs) for signal amplification again. The response of the electrochemical biosensor is linear in the range 0.5-80 fM (0.5, 1.5, 5, 10, 40, 80 fM) with a limit of detection (LOD) of 0.46 fM, using differential pulse voltammetry (DPV) in a potential range of - 100-500 mV. The biosensor was successfully applied to the analysis of serum samples of 14 normal people, 14 mild cognitive impairment (MCI) patients, and 14 dementia patients. Graphical abstract Schematic representation of signal multi-amplified electrochemical biosensor for determination of tau-441 protein in human serum.

ZnO nanowire-based fluorometric enzymatic assays for lactate and cholesterol.

A rapid fluorometric method is described for the determination of lactate and cholesterol by using ZnO nanowires (ZnO NWs). The assay is based on the detection of the hydrogen peroxide generated during the enzymatic reactions of the oxidation of lactate or cholesterol. Taking advantage of the electrostatic interactions between the enzymes and the ZnO NWs, two bioconjugates were prepared by mixing the nanomaterial and the enzymes, viz. lactate oxidase (LOx) or cholesterol oxidase (ChOx). The enzymatically generated hydrogen peroxide quenches the fluorescence of the ZnO NWs, which have emission peaks at 384 nm and at 520 nm under 330 nm photoexcitation. H2O2 quenches the 520 nm band more strongly. Response is linear up to 1.9 µM lactate concentration, and up to 1.1 µM cholesterol concentration. Relative standard deviation was found to be 5%. The detection limits for lactate and cholesterol are 0.54 and 0.24 µM, respectively. Graphical abstractSchematic representation of fluorescence assay based on ZnO nanowires photoluminiscence for lactate and colesterol detection.

Gold nanoparticle-loaded hollow Prussian Blue nanoparticles with peroxidase-like activity for colorimetric determination of L-lactic acid.

The intrinsic peroxidase-like activity of hollow Prussian Blue nanoparticle-loaded with gold nanoparticles (Au@HMPB NPs) were applied to oxidize the substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2 to give a blue-green coloration. The morphology of the Au@HMPB NPs and its peroxidase-mimicking activity was characterized in detail. The catalytic activity follows Michaelis-Menten kinetics and is higher than that of HMPB NPs not loaded with gold nanoparticles. The NPs were employed to detect L-lactic acid colorimetrically (at 450 nm) via detection of H2O2 that is generated during enzymatic oxidation by L-lactate oxidase (LOx). The limit of detection is 4.2 µM. The assay was successfully applied to the quantitation of L-lactic acid in spiker human serum samples. Graphical abstract Gold nanoparticle-loaded hollow Prussian Blue nanoparticles (Au@HMPB NPs) with peroxidase-like catalytic activity can oxidize the substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. The nanoparticles were applied for the detection of L-lactic acid through detection of H2O2 that is generated by L-lactate oxidase (LOx) catalyzed oxidation of L-lactic acid.

Phytic acid doped poly(3,4-ethylenedioxythiophene) modified with copper nanoparticles for enzymeless amperometric sensing of glucose.

A nanocomposite consisting of phytic acid (PA) that was doped with poly(3,4-ethylenedioxy-thiophene) (PEDOT) and modified with copper nanoparticles (CuNPs) was placed on a glassy carbon electrode and then applied in an enzymeless glucose sensor. The undulating PEDOT/PA composite has good conductivity and a large surface area, which was suitable as substrate for the uniform growth of CuNPs. The modified electrode typically operated at a potential near 0.55 V (vs. Ag/AgCl) demonstrated remarkable catalytic activity towards direct oxidation of glucose in NaOH solution (the major limitation of this sensor). Figures of merit include (a) a wide analytical range (5 to 403 µM); (b) high sensitivity (79.27 µA·µM-1·cm-2), (c) a low detection limit (0.28 µM at a signal to noise ratio of 3), and (d) fast response (< 4 s). Graphical abstractA nanocomposite of phytic acid (PA) doped poly(3,4-ethylenedioxy-thiophene) (PEDOT) modified with copper nanoparticles (CuNPs) onto a glassy carbon electrode was prepared by electrochemical strategy. The CuNPs/PEDOT/PA-modified electrodes were applied in enzymeless glucose sensors with high performance.

Redox modulated fluorometric sensing of ascorbic acid by using a hybrid material composed of carbon dots and CoOOH nanosheets.

Carbon dots (CDs) were hydrothermally prepared from gelatin as the sole precursor. The CDs were hybridized with CoOOH nanosheets (NSs) to obtain a fluorescent probe (CD-CoOOH) for ascorbic acid (AA). The blue luminescence of the CDs, with excitation/emission maxima of 350/443 nm, is quenched by the NSs. If the NSs are reduced to Co2+ by addition of AA, the CD-CoOOH hybrid is disintegrated and fluorescence recovers. The hybrid nanoprobe has a linear response in the 0.8-12.5 µM and 12.5-690 µM AA concentration ranges and a 0.025 µM limit of detection. Compared to previously reported methods for detecting AA, this methods has a wider linear range and a lower detection limit. The nanoprobe was utilized to quantify AA in spiked human serum samples and gave satisfactory results. The strategy was also applied to the construction of an "AND" logic gate, which avoided perplexed material decorations and chemical tracking. Graphical abstract Scheme 1. Schematic illustrations of the preparation of CDs and of the working principle for determination of ascorbic acid (AA).

Nanocomposites consisting of copper and copper oxide incorporated into MoS4 nanostructures for sensitive voltammetric determination of bisphenol A.

A nanocomposite (NC) of type Cu/Cu2O/CuO@MoS4 was obtained via coprecipitation and a hydrothermal approach from copper oxide nanoparticles and MoS4 nanostructures. A series of nanocomposites has been fabricated with varying fractions of MoS4. The NCs were characterized by XRD, XPS, SEM and TEM. The synergistic effect of enlarged specific surface, high electrocatalytic activity and the presence of mixed valencies strongly enhance the redox response at the interface of a glassy carbon electrode (GCE) modified with the NC. The intercalation properties of MoS4 in the NCs result in outstanding electro-oxidative performance towards bisphenol A (BPA). The modified GCE, best operated at +0.16 V vs. SCE, has a linear response in the 0.0001 µM to 17 µM BPA concentration range (R2 = 0.998) and high sensitivity (1587 mA µM-1 cm-2). The sensor can detect BPA with very good selectivity, enhanced storage stability and a low detection limit of 0.10 nM (S/N = 3). This is the lowest value among the non-enzymatic biosensors reported until now. The sensor was used for real-time in-vitro monitoring of BPA in (spiked) serum samples. Graphical abstract Schematic representation of Cu/Cu2O/CuO@MoS4 hybrid material fabricated by a hydrothermal method for sensitive determination of bisphenol A (BPA) from biological fluids.

Colorimetric adenosine assay based on the self-assembly of aptamer-functionalized gold nanorods.

A colorimetric method is presented for ultrasensitive determination of adenosine. The assay is based on side-by-side self-assembly of aptamer-functionalized gold nanorods (Au NRs). It relies on the fact that the conjugation of the helper DNA predominantly occurs at the terminal ends of the Au NRs rather than at their sides. The adenosine aptamers consist of two pieces of ssDNA (termed C1 and C2) that were individually attached to the sides of Au NRs. In the presence of adenosine, it will be captured by C1 and C2 to form a stable sandwich structure. As a result, a side-to-side assembly of the Au NRs occurs. If the adenosine concentration is increased, the absorbance of the Au NRs at 742 nm gradually decreases, and the color changes from brick red to dark brown. Response is linear range in the 10 pM to 5 nM adenosine concentration range, and the detection limit is as low as 3.3 pM. Adenosine analogues such as uridine and cytidine do not interfere. The method was used to quantify adenosine in serum samples at concentrations as low as 10 pM. Graphical abstractSchematic representation of an effective colorimetric method for adenosine detection based on target adenosine-induced side-by-side self-assembly of gold nanorods (Au NRs).

A nanocomposite prepared from magnetite nanoparticles, polyaniline and carboxy-modified graphene oxide for non-enzymatic sensing of glucose.

The authors report on the synthesis of carboxy functionalized graphene oxide (fGO) decorated with magnetite (Fe3O4) nanoparticles. The resulting nanomaterial was used to prepare a composite with polyaniline (PANI) which was characterized by UV-vis, Fourier transform-infrared and Raman spectroscopies. Its surface morphologies were characterized by atomic force and scanning electron microscopies. A screen-printed carbon electrode was then modified with the nanocomposite to obtain an enzyme-free glucose sensor. The large surface of fGO and Fe3O4 along with the enhanced charge transfer capability of PANI warrant a pronounced electrochemical response (typically measured at 0.18 V versus Ag/AgCl) which is suppressed in the presence of glucose. This reduction of current by glucose was used to design a sensitive method for quantification of glucose. The response of the modified SPCE is linear in the 0.05 µM - 5 mM glucose concentration range, and the lower detection limit is 0.01 µM. Graphical abstract Schematic illustration of in-situ anchoring of Iron oxide on functionalized graphene oxide and synthesis of its polymeric nanocomposite for non-enzymatic detection of Glucose. The nanocomposite modified screen printed interface enabled monitoring of glucose at lower potential with higher precision. GO (graphene oxide), fGO (functionalized graphene oxide), PANI (polyaniline).