Detection Of Small Organic Molecules Research Articles

Recent Application of Nanopores in the Detection of Small Organic Molecules

Recent Application of Nanopores in the Detection of Small Organic Molecules

One-Pot Preparation of Ratiometric Fluorescent Molecularly Imprinted Polymer Nanosensor for Sensitive and Selective Detection of 2,4-Dichlorophenoxyacetic Acid.

The development of fluorescent molecular imprinting sensors for direct, rapid, and sensitive detection of small organic molecules in aqueous systems has always presented a significant challenge in the field of detection. In this study, we successfully prepared a hydrophilic colloidal molecular imprinted polymer (MIP) with 2,4-dichlorophenoxyacetic acid (2,4-D) using a one-pot approach that incorporated polyglycerol methacrylate (PGMMA-TTC), a hydrophilic macromolecular chain transfer agent, to mediate reversible addition-fragmentation chain transfer precipitation polymerization (RAFTPP). To simplify the polymerization process while achieving ratiometric fluorescence detection, red fluorescent CdTe quantum dots (QDs) and green fluorescent nitrobenzodiazole (NBD) were introduced as fluorophores (with NBD serving as an enhancer to the template and QDs being inert). This strategy effectively eliminated background noise and significantly improved detection accuracy. Uniform-sized MIP microspheres with high surface hydrophilicity and incorporated ratiometric fluorescent labels were successfully synthesized. In aqueous systems, the hydrophilic ratio fluorescent MIP exhibited a linear response range from 0 to 25 μM for the template molecule 2,4-D with a detection limit of 0.13 μM. These results demonstrate that the ratiometric fluorescent MIP possesses excellent recognition characteristics and selectivity towards 2,4-D, thus, making it suitable for selective detection of trace amounts of pesticide 2,4-D in aqueous systems.

How to Improve the Performance of Electrochemical Sensors via Minimization of Electrode Passivation

It follows from critical evaluation of possibilities and limitations of modern voltammetric/amperometric methods that one of the biggest obstacles in their practical applications in real sample analysis is connected with electrode passivation/fouling by electrode reaction products and/or matrix components. This review summarizes possibilities how to minimise these problems in the field of detection of small organic molecules and critically compares their potential and acceptability in practical laboratories. Attention is focused on simple and fast electrode surface renewal, the use of disposable electrodes just for one and/or few measurements, surface modification minimising electrode fouling, measuring in flowing systems, application of rotating disc electrode, the use of novel separation methods preventing access of passivating particles to electrode surface and the novel electrode materials more resistant toward passivation. An attempt is made to predict further development in this field and to stress the need for more systematic and less random research resulting in new measuring protocols less amenable to complications connected with electrode passivation.

Graphene oxide sensors of high sensitivity fabricated using cold atmospheric-pressure hydrogen plasma for use in the detection of small organic molecules

A novel electrochemical sensor was fabricated by means of solution-processed graphene oxide (GO) ink on fluorine-doped tin oxide (FTO), followed by rapid reduction of the GO surface to reduced graphene oxide (rGO) by cold diffuse atmospheric plasma generated in pure hydrogen gas. The FTO/rGO electrode was then employed in the detection of ascorbic acid, uric acid, dopamine, and acetaminophen molecules with low limits of detection; in these cases, 0.03, 0.06, 0.07, and 0.04 μM, respectively. While traditional methods for the reduction of GO are time-consuming, in the order of tens of minutes, and involve high-temperature (450 °C) sintering in argon, the novelty of this work lies in the rapid manufacture of the sensing material through cold plasma-assisted reduction of a GO surface. Since the temperature of the plasma procedure is below 70 °C, with the elapsed time lesser than 10 s, and the plasma unit is capable of processing an area of up to 160 cm2, FTO/rGO electrode preparation can be performed at high throughput. This fabrication method may be easily deployed in rapid and low-cost roll-to-roll manufacture, a factor essential for the future commercialization of cost-effective flexible and printed electronics based on a wide range of sensors.

Electric Charge Detection of Sparse Organic Acid Molecules Using an Organic Field-Effect Transistor (OFET)-Based Sensor

Abstract Detection and measurement of organic acids, such as small carboxylic acids, are useful for quality control of processed food and drinks and in the healthcare sector. Previously, chromatographic and electrophoresis methods requiring a bench-top device were used for their detection. In this article, we report an organic field-effect transistor (OFET)-based sensor capable of sensing electrical changes, which was applied to the detection of citric acid, chosen as a small organic acid model. When citric acid was injected into the OFET-sensor equipped with a nickel-nitrilotriacetic acid-immobilized gold-electrode (Ni-NTA-immobilized Au-electrode), the shifts of the OFET transfer characteristic curves were observed to depend on the citric acid concentration, in the range from 0 to 1000 µM. On the other hand, there was no response after citric acid addition in the case of a quartz-crystal microbalance (QCM)-sensor, which is a mass-sensitive device, under similar low-salt conditions because the mass change on the sensor surface was below the detection limit of the QCM device owing to inter-anion repulsions. OFET-sensors have advantages in the detection of small organic molecules with an electro-charged group as well as the possibility to be incorporated into portable devices in the future.

Application of mesocellular siliceous foams (MCF) for surface-assisted laser desorption ionization mass spectrometry (SALDI-MS) Analysis of fingermarks

Recent advances in nanotechnology applied in forensic sciences have contributed to consider new approaches including chemical evaluation of latent fingermarks. Significant improvement to the detection of small organic molecules has been reached with matrix-free methods associated to laser desorption/ionization mass spectrometry. The present study investigated the application of mesocellular siliceous foam (MCF) as an ionizing agent for laser desorption/ionization (LDI-MS) analysis of fingermarks as a proof of concept research. Fingermarks from three different donors were deposited directly onto a MALDI target plate and α-CHCA matrix solution, MCF ethanolic suspension or MCF/magnetic powder mixture were used for treatment. Microscopy characterization of MCF support showed particles with irregular morphology and variable sizes, and a unordered porous surface with pores diameter ranging from about 10 to 20 nm. Results showed less intense peaks in the spectra produced by the MCF support (control). Analysis of fingermarks showed ions related to endogenous and exogenous molecular components, including possible lipids from human sebum and quaternary ammonium cations commonly present in cosmetics. Promising and reproducible results were obtained for the fingermarks dusted with the MCF/magnetic powder mixture. Considering the forensic applications of nanomaterials for the analysis of small molecules in biological samples by matrix-free LDI techniques, the advantages of silica based materials should be further investigated.

D-A-D type dinitriles with vapor-dependent luminescence in the solid state

D-A-D (Donor-Acceptor-Donor) type dinitriles linked by a styryl or phenylethynyl group have been prepared. These groups were introduced to increase the flexibility and the size of the π-conjugation in the chromophores. Both compounds showed strong emission in the solid state, AIE (aggregation-induced emission) behavior, and mechanochromism. The fluorescence color of ground powder changed by organic solvent vapor (vapochromism). Especially, the emission color of the styryl dinitrile after exposures depends on the solvent, while that of the phenylethynyl dinitrile is the same after exposure to different solvents. These results were explained by single crystal and powder XRD measurements, which revealed that the flexible styryl linker leads to a loose crystal packing, resulting in a dinitrile with multi-state microcrystalline structures. This methodology based on the flexible linker allows for the detection of small organic molecules without transition metals.

Study on the SERS substrate composed of Au@Ag core-shell nanoparticles linked to SiO2 spheres

ABSTRACTWe have developed a sensitive surface-enhanced Raman scattering (SERS) substrate composed of 60-nm Au@Ag core-shell nanoparticles linked to 360-nm SiO2 sphere base, which experimentally demonstrated that the detection limits for p-aminothiophenol (PATP), Rhodamine 6G (R6G) and 5,5-dithiobis(2-dinitrobenzoic acid) (DTNB) could be 10−13, 10−13 and 10−12 M, respectively. The fabrication method of the SERS substrate and the experimental investigation on the enhancement performance of the substrate are presented in detail in this article. The results show that the 360 nm SiO2-60 nm Au@Ag nanocomposites could be used as an excellent substrate for SERS detection of small organic molecules.

Luminescent coordination polymers based on a new resorcin[4]arene-functionalized tetracarboxylate: Highly selective luminescent detection of metal cations, anions and small organic molecules

Fluorescence-based probes have received considerable attention because of their superiority in high selectivity and sensitivity. In this work, two novel luminescent isostructural coordination polymers (CPs), namely, [Zn3(HL)2(DMF)2(H2O)2]·2H2O (1) and [Cd3(HL)2(DMF)2(H2O)2]·2H2O (2), were successfully prepared by using a new resorcin[4]arene-based tetracarboxylic acid H4L under solvothermal conditions. In 1 and 2, HL3- anions bridge four metal cations to form charming 2D double layer structures. Drastically, the highly selective and sensitive luminescent detection of small organic molecules, metal cations and anions, particularly of Fe3+, Cr2O72- and nitrobenzene, has been studied using 1 or 2 as a promising luminescent sensor.

Label-Free Detection of Small Organic Molecules by Molecularly Imprinted Polymer Functionalized Thermocouples: Toward In Vivo Applications.

Molecularly imprinted polymers (MIPs), synthetic polymeric receptors, have been combined successfully with thermal transducers for the detection of small molecules in recent years. However, up until now they have been combined with planar electrodes which limits their use for in vivo applications. In this work, a new biosensor platform is developed by roll-coating MIP particles onto thermocouples, functionalized with polylactic acid (PLLA). As a first proof-of-principle, MIPs for the neurotransmitter dopamine were incorporated into PLLA-coated thermocouples. The response of the synthetic receptor layer to an increasing concentration of dopamine in buffer was analyzed using a homemade heat-transfer setup. Binding of the template to the MIP layer blocks the heat transport through the thermocouple, leading to less heat loss to the environment and an overall higher temperature in the measuring chamber. The measured temperature increase is correlated to the neurotransmitter concentration, which enables measurement of dopamine levels in the micromolar regime. To demonstrate the general applicability of the proposed biosensor platform, thermocouples were functionalized with similar MIPs for cortisol and serotonin, indicating a similar response and limit-of-detection. As the platform does not require planar electrodes, it can easily be integrated in, e.g., a catheter. In this way, it is an excellent fit for the current niche in the market of therapeutics and diagnostics. Moreover, the use of a biocompatible and disposable PLLA-layer further illustrates its potential for in vivo diagnostics.

Fluorescent Aromatic Tag-Functionalized MOFs for Highly Selective Sensing of Metal Ions and Small Organic Molecules.

By varying the fluorescent tags of resorcin[4]arene-based tetracarboxylic acids from phenyl to naphthyl, two highly luminescent metal-organic frameworks (MOFs), namely, [Zn2(TPC4A)(DMF)(H2O)4]·3H2O (1) and [(CH3)2NH2]2[Zn(TNC4A)]·4H2O (2), were successfully achieved (TPC4A = 2,8,14,20-tetra-phenyl-6,12,18,24-tetra-methoxy-4,10,16,22-tetra-carboxy-methoxy-resorcin[4]arene and TNC4A = 2,8,14,20-tetra-1-naphthal-6,12,18,24-tetra- methoxy-4,10,16,22-tetra-carboxy-methoxy-resorcin[4]arene). Compound 1 features a unique 2D network, while 2 exhibits a fascinating 3D framework. The highly selective detection of small organic molecules as well as Fe(2+) and Fe(3+) was performed for 1 and 2 as fluorescent sensors. Remarkably, luminescent 1 and 2 were used as sensory materials for the sensing of various amine vapors with high selectivity and rapid response. Most strikingly, clear fluorescence "on-off" switch-functions toward small organic molecules as well as amine vapors were also explored for luminescent 1 and 2.

A chemiluminescence assay for L-histidine based on controlled DNAzyme catalytic reactions on magnetic microparticles

We describe a chemiluminescence (CL) assay for L-histidine that is based on the use of DNAzyme covalently immobilized on 1.5-μm sized magnetic beads. On addition of a substrate labeled with a CL reagent, the DNAzyme and substrate form a stable duplex by allosteric synergetic stabilization of each duplex. If L-histidine is added to this system, self-cleavage of the substrate occurs through catalytic reaction and results in the formation of two fragments which dissociate from the beads. After removal of the magnetic beads, the labeled fragments can be detected by CL whose intensity is linearly related to the concentration of L-histidine in the 1.0 to 1,000 nM range. The detection limit is 0.3 nM, and the RSD is 3.4 % at a 50 nM level (n = 9). The method has been successfully applied to the determination of L-histidine in spiked human serum samples and holds promise as a widely applicable general platform for DNAzyme-based CL detection of small organic molecules and of metal ions.

Thermal detection of histamine with a graphene oxide based molecularly imprinted polymer platform prepared by reversible addition–fragmentation chain transfer polymerization

Graphene oxide (GO), with its small dimension and high surface-to-volume ratio, can enhance the binding capacity and sensitivity of molecularly imprinted polymers (MIPs). Therefore, a straightforward and fast method was developed to graft MIPs onto GO by reversible addition–fragmentation chain transfer (RAFT) polymerization. First, the initiator was linked to the GO in a simple two-step process which was verified via UV–vis spectroscopy. Subsequently, a MIP layer for histamine was grown onto the functionalized surface by RAFT crosslinking polymerization, enabling control over the imprint structure. The formation of a hybrid GO–MIP structure, particles surrounded with a polymer network of ∼2.4nm thick, was verified by atomic force microscopy (AFM). Classical batch rebinding experiments demonstrated the specificity of the MIP towards its original template histamine. Next, the heat-transfer method (HTM) was applied, a novel sensing technique requiring only two thermocouples and an adjustable heat source. This method has been employed for the detection of small organic molecules with bulk MIPs, but never with a GO-hybrid structure. For proof-of-principle purposes, silicon substrates were functionalized with the GO–MIPs and sensing was performed on histamine in buffer solutions. The designed sensor platform could detect histamine in the nanomolar regime, similar to conventional techniques. In summary, we have developed a fast and straightforward method to prepare MIP–GO hybrids which were able to measure histamine in buffer solutions by thermal detection. Since GO exhibits excellent thermal properties, this opens the window to sensing of small organic molecules in relevant biological samples.

Array formatting of the heat-transfer method (HTM) for the detection of small organic molecules by molecularly imprinted polymers.

In this work we present the first steps towards a molecularly imprinted polymer (MIP)-based biomimetic sensor array for the detection of small organic molecules via the heat-transfer method (HTM). HTM relies on the change in thermal resistance upon binding of the target molecule to the MIP-type receptor. A flow-through sensor cell was developed, which is segmented into four quadrants with a volume of 2.5 μL each, allowing four measurements to be done simultaneously on a single substrate. Verification measurements were conducted, in which all quadrants received a uniform treatment and all four channels exhibited a similar response. Subsequently, measurements were performed in quadrants, which were functionalized with different MIP particles. Each of these quadrants was exposed to the same buffer solution, spiked with different molecules, according to the MIP under analysis. With the flow cell design we could discriminate between similar small organic molecules and observed no significant cross-selectivity. Therefore, the MIP array sensor platform with HTM as a readout technique, has the potential to become a low-cost analysis tool for bioanalytical applications.

Surface-assisted laser desorption ionization mass spectrometry techniques for application in forensics.

Matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS) is an excellent analytical technique for the rapid and sensitive analysis of macromolecules (>700 Da), such as peptides, proteins, nucleic acids, and synthetic polymers. However, the detection of smaller organic molecules with masses below 700 Da using MALDI-MS is challenging due to the appearance of matrix adducts and matrix fragment peaks in the same spectral range. Recently, nanostructured substrates have been developed that facilitate matrix-free laser desorption ionization (LDI), contributing to an emerging analytical paradigm referred to as surface-assisted laser desorption ionization (SALDI) MS. Since SALDI enables the detection of small organic molecules, it is rapidly growing in popularity, including in the field of forensics. At the same time, SALDI also holds significant potential as a high throughput analytical tool in roadside, work place and athlete drug testing. In this review, we discuss recent advances in SALDI techniques such as desorption ionization on porous silicon (DIOS), nano-initiator mass spectrometry (NIMS) and nano assisted laser desorption ionization (NALDI™) and compare their strengths and weaknesses with particular focus on forensic applications. These include the detection of illicit drug molecules and their metabolites in biological matrices and small molecule detection from forensic samples including banknotes and fingerprints. Finally, the review highlights recent advances in mass spectrometry imaging (MSI) using SALDI techniques.

Immunological Detection of Small Organic Molecules in the Presence of Perchlorates: Relevance to the Life Marker Chip and Life Detection on Mars

The proposed ExoMars mission, due to launch in 2018, aims to look for evidence of extant and extinct life in martian rocks and regolith. Previous attempts to detect organic molecules of biological or abiotic origin on Mars have been unsuccessful, which may be attributable to destruction of these molecules by perchlorate salts during pyrolysis sample extraction techniques. Organic molecules can also be extracted and measured with solvent-based systems. The ExoMars payload includes the Life Marker Chip (LMC) instrument, capable of detecting biomarker molecules of extant and extinct Earth-like life in liquid extracts of martian samples with an antibody microarray assay. The aim of the work reported here was to investigate whether the presence of perchlorate salts, at levels similar to those at the NASA Phoenix landing site, would compromise the LMC extraction and detection method. To test this, we implemented an LMC-representative sample extraction process with an LMC-representative antibody assay and used these to extract and analyze a model sample that consisted of a Mars analog sample matrix (JSC Mars-1) spiked with a representative organic molecular target (pyrene, an example of abiotic meteoritic infall targets) in the presence of perchlorate salts. We found no significant change in immunoassay function when using pyrene standards with added perchlorate salts. When model samples spiked with perchlorate salts were subjected to an LMC-representative liquid extraction, immunoassays functioned in a liquid extract and detected extracted pyrene. For the same model sample matrix without perchlorate salts, we observed anomalous assay signals that coincided with yellow coloration of the extracts. This unexpected observation is being studied further. This initial study indicates that the presence of perchlorate salts, at levels similar to those detected at the NASA Phoenix landing site, is unlikely to prevent the LMC from extracting and detecting organic molecules from martian samples.

An Electronic, Aptamer-Based Small-Molecule Sensor for the Rapid, Label-Free Detection of Cocaine in Adulterated Samples and Biological Fluids

Whereas spectroscopic and chromatographic techniques for the detection of small organic molecules have achieved impressive results, these methods are generally slow and cumbersome, and thus the development of a general means for the real-time, electronic detection of such targets remains a compelling goal. Here we demonstrate a potentially general, label-free electronic method for the detection of small-molecule targets by building a rapid, reagentless biosensor for the detection of cocaine. The sensor, based on the electrochemical interrogation of a structure-switching aptamer, specifically detects micromolar cocaine in seconds. Because signal generation is based on binding-induced folding, the sensor is highly selective and works directly in blood serum and in the presence of commonly employed interferents and cutting agents, and because all of the sensor components are covalently attached to the electrode surface, the sensor is also reusable: we achieve >99% signal regeneration upon a brief, room temperature aqueous wash. Given recent advances in the generation of highly specific aptamers, this detection platform may be readily adapted for the detection of other small molecules of a wide range of clinically and environmentally relevant small molecules.

Sensors made of RNA: tailored ribozymes for detection of small organic molecules, metals, nucleic acids and proteins

Nucleic acids are well suited to serve as biosensors for the fast and reliable detection of small organic molecules, such as a number of metabolites or antibiotics, specific nucleic acid sequences, peptides, proteins or metal ions. One of the main advantages of using nucleic acids as biosensors is that they can be modulated to respond allosterically to specific effectors. Thus molecular recognition is transformed directly into a catalytic process with observable results. In particular, catalytic RNA structures, such as the hammerhead and hairpin ribozymes, have been used for biosensor engineering. The review reports on the function mode of nucleic acid biosensors and introduces recent developments and applications in the field.