Target Analytes In Solution Research Articles

Synthesis of length-tunable DNA carriers for nanopore sensing.

Molecular carriers represent an increasingly common strategy in the field of nanopore sensing to use secondary molecules to selectively report on the presence of target analytes in solution, allowing for sensitive assays of otherwise hard-to-detect molecules such as small, weakly-charged proteins. However, existing carrier designs can often introduce drawbacks to nanopore experiments including higher levels of cost/complexity and carrier-pore interactions that lead to ambiguous signals and elevated clogging rates. In this work, we present a simple method of carrier production based on sticky-ended DNA molecules that emphasizes ease-of-synthesis and compatibility with nanopore sensing and analysis. In particular, our method incorporates the ability to flexibly control the length of the DNA carriers produced, enhancing the multiplexing potential of this carrier system through the separable nanopore signals they could generate for distinct targets. A proof-of-concept nanopore experiment is also presented, involving carriers produced by our method with multiple lengths and attached to DNA nanostructure targets, in order to validate the capabilities of the system. As the breadth of applications for nanopore sensors continues to expand, the availability of tools such as those presented here to help translate the outcomes of these applications into robust nanopore signals will be of major importance.

Tip enrichment surface-enhanced Raman scattering based on the partial Leidenfrost phenomenon for the ultrasensitive nanosensors

Surface-enhanced Raman scattering (SERS) possesses the advantage that directly detects target analytes in solution with high specificity and sensitivity without complicated pretreatment procedures. It remains a challenge in most practical applications to achieve molecule sensitivity in any highly diluted solutions. Here, we develop a robust and practical molecular enrichment strategy that can effectively confine analyte molecules and Au nanoparticles together in a short time into a small-sized sensitive region on a needle tip, based on the Leidenfrost phenomenon and capillary force. In this strategy, the Leidenfrost evaporation phenomenon maintains the analytes droplet in a Cassie state based on a levitating force, and at the same time, a hung needle tip anchors the droplet based on the capillary force. After 1–2 min quick evaporation, more than 98% Au nanoparticles and analytes can be condensed into an around 0.5 mm small size area on the needle tip. Due to the significant enrichment capability and reproducibility, the SERS measurement enables to achieve the limit of detection (LOD) down to 0.08 nM (at an S/N ratio of 3) for crystal violet (CV) molecules and to nM level for several types of pesticide molecules (glyphosate, carbendazim, thiram and choline) in ethanol solution. The strategy was also applied to the detection of CV molecules in mixture pigments solution, thiram in spiked environment water samples, with good selectivity and sensitivity. In addition, using the high thermal conductivity substrate without additional surface modification, this enrichment SERS detection may open the possibility of universal applications due to its facile and cost-effective. The accurate site of the needle tip offers great practical potentials for on-site identification by using a handheld Raman spectrometer.

Molecular antenna tailored organic thin-film transistors for sensing application

By tailoring the neighboring-conductive-channel organic layer using a plasma-assisted-interfacial-grafting method, we introduced a molecular antenna on the surface of organic transistors to enable direct interaction between the semiconductors in the conductive channel and the target analytes in solution.

Surface Enhanced Raman Scattering and Gated Materials for Sensing Applications: The Ultrasensitive Detection of Mycoplasma and Cocaine.

We present herein a novel combination of gated mesoporous silica nanoparticles (MSNs) and surface-enhanced Raman scattering (SERS) for sensing applications. As a proof-of-concept, we show the design of a system comprising MSNs loaded with crystal violet (CV), a molecule with high Raman cross section acting as SERS reporter, and capped with either a suitable DNA sequence for the detection of Mycoplasma genomic DNA or with an aptamer that selectively coordinates cocaine. In both cases the presence of the corresponding target analyte in solution (i.e., genomic DNA or cocaine) resulted in the release of CV. CV delivery was detected by SERS upon adsorption on gold nanotriangles (AuNTs), which display an efficient electromagnetic field enhancement and a high colloidal stability. By using this novel procedure a limit of detection of at least 30 copies DNA per μL was determined for the detection of Mycoplasma genomic DNA, whereas cocaine was detected at concentrations as low as 10 nm.

Three‐Dimensional Interdigitated Electrode Array as a Tool for Surface Reactions Registration

AbstractPossible applications of a new transducer based on a three dimensional interdigitated electrode array (3D‐IDEA) with electrode digits separated by an insulating barrier are discussed. Due to the presence of insulating barriers that separate the adjacent digits of the electrodes the main portion of the probing electrical current goes close to the surface of the barrier. Chemical modification of the barrier surface with the probe molecules permits to realise direct detection of subsequent target analytes in solution. The functional mechanism of the device is based on registration of changes in conductivity at the surface of the barrier provoked by electrical charge redistribution caused by surface chemical reactions. Three‐dimensional sensor shows considerable improvement in sensitivity compared with a standard planar IDEA design sensors. The potential of the developed device as a sensor transducer to detect various chemical and bio chemical reactions is demonstrated. Examples include enzyme immobilisation, polyelectrolytes layer‐by‐layer deposition, covalent chemical modification with molecules containing reactive thiol groups.

Microcantilever Biosensors: Probing Biomolecular Interactions at the Nanoscale

Microcantilever based biosensors have attracted much attention as a label-free, real-time and highly sensitive approach to the detection of biomolecules. When specific biomolecular interactions occur between a receptor immobilized on one side of a cantilever and a target analyte in solution, a mechanical bending of the cantilever results due to a change in surface stress, thereby translating biochemical interactions into a concentration-dependent nanomechanical response of the microcantilevers. In this review, we present a general overview of the operation principles, fabrication and preparation of microcantilever biosensors and discuss their uses for a wide range of biosensing applications. The focus of the review is given to probing the biomolecular interactions at the solid-liquid interface by measuring the cantilever bending. In addition to the label-free detection of DNA, protein and cells, the emphasis is also made to discuss about the new development of microcantilever biosensors for label-free probing nanoscale conformational changes of DNA, protein and polymers, and real-time detection of nanomechanical forces from living cells. Finally, the outlook for future development work and challenges is also discussed. Keywords: Microcantilever biosensors, molecular interactions, conformational changes, microarrays, ELISAs, atomic force microscopy (AFM), label-free biosensor, microfabrication, Device Fabrication, AFM, Surface Functionalization, BIOSENSING APPLICATIONS, DNA hybridization reaction, single nucleo-tide polymorphisms (SNPs),, prostate-specific antigen (PSA), human serum albumin, human plasminogen, CDK2, drug vancomycin, mucopetide analogues, piezoelectric cantilever

A comparison of direct thermal desorption with solvent extraction for gas chromatography-mass spectrometry analysis of semivolatile organic compounds in diesel particulate matter

Direct thermal desorption-gas chromatography-mass spectrometry (DTD-GC-MS) is a technique that is finding application in the characterisation of the semivolatile organic carbon fraction of ambient and combustion source particulate matter (PM) collected on filters. In this study, three DTD-GC-MS methods were assessed and compared to a conventional solvent extraction method for analysis of a mixture of target analytes in solution and of diesel PM collected on quartz filters. The target analytes included n-alkanes, hopanes, steranes and polycyclic aromatic hydrocarbons. This study showed that while the three DTD-GC-MS methods were generally comparable to the solvent extraction method, (1) the choice of calibration strategy and calibration materials has a significant impact on the measured accuracy of a method; (2) very large variations were seen in all methods for the more volatile compounds such as C10 to C13 n-alkanes and naphthalene; (3) accuracy, defined as difference from the known concentration of a liquid sample, ranged from 5% to 32%; (4) precision, defined as the relative standard deviation, ranged from 4% to 16%. The average difference of DTD-GC-MS results from the solvent extraction results for the diesel PM filters ranged from 20% to 40%. This difference was driven by the large number of target analytes present at relatively low concentrations (<25 pg/mm2) and their corresponding higher variability. Differences in performance among the compound classes were noted. Minimum detection limits for the DTD-GC-MS methods were on the order of 0.1 to 1 pg/mm2 and were as good as or better than those obtained for the solvent extraction method.