Detection Of Ultra-low Levels Research Articles

Overview of nano enabled sensor for analysis of explosive substances

Threats of armed conflict and terrorist attacks present difficult challenges for defense agencies around the world and are an increasing source of worry for the public and security-conscious policymakers. The environmental monitoring of residue or discarded explosives in soil, as well as the detection of ultra-low levels of explosive compounds in remote areas or under extreme conditions for anti-terrorist activities, continue to pose significant challenges. Most explosives produce very little vapors, making it difficult to detect them with common techniques for other compounds. Due to a number of factors, including the large variety of explosives substances, the enormous number of deployment methods, and the dearth of low-cost sensors with high sensitivity and selectivity makes explosive detection very complicated and expensive task. To defeat explosives-based terrorism, sensors must have high sensitivity and selectivity as well as the capacity to produce and deploy them at lower costs. Nanotechnology-based sensors have an excellent possibility of meeting all the criteria for a successful approach to explosive trace detection. The design and analytical capabilities of explosive detection systems employing nanomaterial as signal transducers are covered in this overview. The review article also discusses the importance of nano-enabled technologies for the explosive detection in security applications, gives background on the technology, and identifies other issues that need to be resolved.

Fabrication of GQD-Electrodeposited Screen-Printed Carbon Electrodes for the Detection of the CRP Biomarker.

The traditional three-electrode electrochemical system used in the development of biosensors for detecting various biomarkers of interest necessitates the use of bulk electrodes, which precludes the deployment of handheld electrochemical devices in clinical applications. Affordable screen-printed carbon electrodes (SPCEs) modified with functional interfaces are being developed to enhance the sensitivity of a compact sensing system as a whole. In this work, SPCEs were fabricated on an overhead projection (OHP) sheet in three different active areas of 2 × 2, 3 × 3, and 4 × 4 mm2 using a screen printing technique, and then ∼2 nm sized graphene quantum dots (GQDs) were electrodeposited over the SPCE surface to add functionality for the detection of ultralow levels of one of the cardiac biomarkers, C-reactive protein (CRP). The proposed mediator-dependent voltammetric biosensor exhibited good sensitivity, a low detection limit, and a linear range of 2.45 μA ng–1 mL–1 cm–2, 0.036 ng mL–1, and 0.5–10 ng mL–1, respectively. The fabricated SPCE/GQDs/anti-CRP biosensor could rapidly detect CRP in less than 25 s. The intra- and interassays were performed with five sensor strips, which showed a minimum standard deviation of 1.85 and 2.8%, respectively. The SPCE/GQDs/anti-CRP electrode was used to detect CRP concentrations in a ringer lactate solution. Thus, the developed biosensor has all of the characteristics such as rapidity, inexpensive disposable electrodes, miniaturization, and a lower detection limit needed to evolve as a point-of-care (PoC) application.

A simple magnetic nanoparticle-poly-enzyme nanobead sandwich assay for direct, ultrasensitive DNA detection.

A simple magnetic nanoparticle (MNP)-poly-enzyme nanobead sandwich assay for direct detection of ultralow levels of unlabeled target-DNA is developed. This approach uses a capture-DNA covalently linked to a dense PEGylated polymer encapsulated MNP and a biotinylated signal-DNA to sandwich the target-DNA. A DNA ligation is then followed to offer high discrimination between the perfect-match and single-base mismatch target-DNAs. Only the presence of a perfect-match target can covalently link the biotinylated signal-DNA onto the MNP surface for subsequent binding to a polymer nanobead tagged with thousands of copies of high-activity neutravidin-horseradish peroxidase (NAV-HRP) for great enzymatic signal amplification. Combining the advantages of the dense MNP surface PEGylation to reduce non-specific adsorption (assay background) and the powerful signal amplification of poly-enzyme nanobead, this assay can directly quantify the target-DNA down to single digit attomolar with a large linear dynamic range of 5 orders of magnitude (from 10-18 to 10-13M).

Highly Sensitive and Selective Detection of Arsenic Using Electrogenerated Nanotextured Gold Assemblage.

Arsenic is considered as a toxic heavy metal which is highly detrimental to ecological systems, and long-term exposure to it is highly dangerous to life as it can cause serious health effects. Timely detection of traces of active arsenic (As3+) is very crucial, and the development of simple, cost-effective methods is imperative to address the presence of arsenic in water and food chain. Herein, we present an extensive study on chemical-free electrogenerated nanotextured gold assemblage for the detection of ultralow levels of As3+ in water up to 0.08 ppb concentration. The gold nanotextured electrode (Au/GNE) is developed on simple Au foil via electrochemical oxidation–reduction sweeps in a metal-ion-free electrolyte solution. The ultrafine nanoscale morphological attributes of Au/GNE substrate are studied by scanning electron microscopy. Square wave anodic stripping voltammetry (ASV) response for different concentrations of arsenites is determined and directly correlated with As3+ detection regarding the type of electrolyte solution, deposition potential, and deposition time. The average of three standard curves are linear from 0.1 ppb up to 9 ppb (n = 15) with a linear regression coefficient R2 = 0.9932. Under optimized conditions, a superior sensitivity of 39.54 μA ppb–1 cm–2 is observed with a lower detection limit of 0.1 ppb (1.3 nM) (based on the visual analysis of calibration curve) and 0.08 ppb (1.06 nM) (based on the standard deviation of linear regression). Furthermore, the electrochemical Au/GNE is also applicable for arsenic detection in a complex system containing Cu2+, Ni2+, Fe2+, Pb2+, Hg2+, and other ions for the selective and sensitive analysis. Au/GNE substrate also possesses remarkable reproducibility and high stability for arsenic detection during repeated analysis and thus can be employed for prolonged applications and reiterating analyses. This electrochemically generated nanotextured electrode is also applicable for As3+ detection and analysis in a real water sample under optimized conditions. Therefore, fabrication conditions and analytical and electroanalytical performances justify that because of its low cost, easy preparation method and assembly, high reproducibility, and robustness, nanosensor Au/GNE can be scaled up for further applications.

Multiplexed surface plasmon imaging of serum biomolecules: Fe3O4@Au Core/shell nanoparticles with plasmonic simulation insights

Nano-biosensors that are not only sensitive and selective, but also enable multiplex detection of ultra-low levels of both large and small biomolecules in clinical sample matrices are essential for in vitro diagnostics. We present herein a multiplex surface plasmon microarray design that employs citrate-stabilized Fe3O4@Au core/shell nanoparticles (NPs) as the plasmon signal amplification label for combined detection of serum proteins and nucleotide markers. The multiplex sensing is demonstrated using two interleukins (IL-6 and IL-8) and two microRNAs (miRNA-21 and miRNA-155) in 10% serum, which is clinically relevant than simple buffer solution based biosensors. We observed that the surface plasmon signal change for larger proteins even at higher concentrations was less than the relatively smaller miRNA molecules. We draw two conclusions from this result: (i) the number of selectively bound analytes onto the sensor (i.e., antigen for an antibody or miRNA for a capture nucleotide) influences the signal change, and (ii) the extent of interaction of the detection probe carrying core/shell NP labels with the sensor surface plasmons influences the amount of signal change. Results indicate that both factors, (i) and (ii), are greater for small oligonucleotide hybridization assembly than a large sandwich protein immunoassembly. The core/shell NPs offered several fold enhanced sensitivity and wider dynamic range of detection over assays without using them. With recently growing attention on in vitro diagnostics for painless/minimally-invasive detection of diseases and abnormalities, findings presented herein are important for designing novel multiplex biosensors for real sample analysis in complex matrices.

A field-deployable surface-enhanced Raman scattering (SERS) method for sensitive analysis of silver nanoparticles in environmental waters

The proliferation of silver nanoparticles (AgNPs) in the environment and resultant transport into aquatic systems have raised concerns regarding their potential toxicity to various organisms. These environmental and ecological concerns demand reliable AgNP detection methods which can measure environmentally relevant quantities of AgNPs in real aquatic systems. This study developed a method that couples a rapid vacuum filtration technique with a portable Raman spectrometer to achieve on-site detection of ultra-low levels of AgNPs in typical and complex aquatic systems. To extract and detect AgNPs, aluminum chloride and ferbam were added for AgNP aggregation and labelling, respectively. The AgNP aggregates were filtered through a membrane, and their presence and quantity were determined based upon the surface-enhanced Raman scattering (SERS) peak intensity of ferbam. Under the optimized conditions, the extraction efficiencies are 99 ± 0.001% in ultrapure water and 98 ± 0.025% in marine water for 1 mg/L AgNPs. This method enables simple volume adjustment and improves the consistency of AgNP distribution on the membrane. The performance of the method was evaluated in different environmental waters, including marine water, fresh waters (pond water, river water, and reservoir outlet water) and drinking waters (municipal tap water and well water), with highest signal intensity in marine water and lowest signals in fresh waters. The signal intensity difference was suggested to be caused by the amount of natural organic matter (NOM) in these environmental waters. Using pond water as an example, the interference was minimized by changing the aggregating salt from AlCl3 to MgCl2, and AgNPs as low as 5 μg/L were reliably detected with a volume of 100 mL. At the same volume, the developed method was sensitive enough to detect 1 μg/L AgNPs in marine water and also holds promise for assessing the time-dependent transformation of AgNPs.

P24 revisited: a landscape review of antigen detection for early HIV diagnosis.

: Despite major advances in HIV testing, early detection of infection at the point of care (PoC) remains a key challenge. Although rapid antibody PoC and laboratory-based nucleic acid amplification tests dominate the diagnostics market, the viral capsid protein p24 is recognized as an alternative early virological biomarker of infection. However, the detection of ultra-low levels of p24 at the PoC has proven challenging. Here we review the landscape of p24 diagnostics to identify knowledge gaps and barriers and help shape future research agendas. Five hundred and seventy-four research articles to May 2018 that propose or evaluate diagnostic assays for p24 were identified and reviewed. We give a brief history of diagnostic development, and the utility of p24 as a biomarker in different populations such as infants, the newly infected, those on preexposure prophylaxis and self-testers. We review the performance of commercial p24 assays and consider elements such as immune complex disruption, resource-poor settings, prevalence, and assay antibodies. Emerging and ultrasensitive assays are reviewed and show a number of promising approaches but further translation has been limited. We summarize studies on the health economic benefits of using antigen testing. Finally, we speculate on the future uses of high-performance p24 assays, particularly, if available in self-test format.

CdTe amplification nanoplatforms capped with thioglycolic acid for electrochemical aptasensing of ultra-traces of ATP

A “signal off” voltammetric aptasensor was developed for the sensitive and selective detection of ultra-low levels of adenosine triphosphate (ATP). For this purpose, a new strategy based on the principle of recognition-induced switching of aptamers from DNA/DNA duplex to DNA/target complex was designed using thioglycolic acid (TGA)-capped CdTe quantum dots (QDs) as the signal amplifying nano-platforms. Owing to the small size, high surface-to-volume ratio and good conductivity, quantum dots were immobilized on the electrode surface for signal amplification. In this work, methylene blue (MB) adsorbed to DNA was used as a sensitive redox reporter. The intensity of voltammetric signal of MB was found to decrease linearly upon ATP addition over a concentration range of 0.1nM to 1.6μM with a correlation coefficient of 0.9924. Under optimized conditions, the aptasensor was able to selectively detect ATP with a limit of detection of 45pM at 3σ. The results also demonstrated that the QDs-based amplification strategy could be feasible for ATP assay and presented a potential universal method for other small biomolecular aptasensors.

Designing of a novel gold nanodumbbells SERS substrate for detection of prohibited colorants in drinks

It is reported that the use of gold nanodumbbells as surface-enhanced Raman spectroscopy (SERS) substrates for the detection of ultra-low levels of four different food colorants: sunset yellow, lemon yellow, orange II and chrysoidin. Gold nanodumbbells are suitable to on-site detection because which have a λmax of 785nm that tune the surface plasmon resonance of the nanoparticles to the laser excitation wavelength of the Raman spectrometer equipped with a 785nm diode laser. In order to investigate the on-site application of the gold nanodumbbells substrate, four pigments in the orange juice and coke were detected by the portable Raman instrument. The results showed that this novel SERS platform can be used as an effective method in detecting prohibited additive colorants in food. This SERS platform provides valuable and powerful analytical tool in real-world applications in food analysis.

SWCNT-aminopolymer composites on mesoporous alumina for fast, room-temperature detection of ultra-low concentrations of NO2 by mediation of water vapour

Fabrication of devices that operate at room temperature and detect ultra low levels of gases such as ammonia, nitrogen dioxide and organic vapours could greatly benefit environment monitoring, medical diagnosis, security implementation and disease prevention. Although single-walled carbon nanotubes (SWCNT) and graphene are materials with great potential for such measurements, fundamental deficiencies such as low selectivity and long recovery time (up to 12h) have prevented their use in practical devices. Here we show that the SWCNT-aminopolymer thin films deposited on alumina membranes can be used for fast and highly reproducible detection of ultra-low levels (down to five parts billion) of nitrogen dioxide at room temperature by the mediation of water vapour. The sensitivity, response time and recovery time of NO2 molecules are found to be sensitive to polar solvent vapours such as water. Using this property, we obtain a reproducible dynamic baseline, different from the traditionally used dry air (or dry nitrogen) baseline, for the detection of NO2 gas. The chemiresistors of SWCNT composited with amino polymers showed higher sensitivity to NO2 in comparison to SWCNT-only chemiresistors fabricated similarly. They showed very small responses to 100ppm NH3 and 100ppm CO in air. The present non-conventional measurement method that exploits the interaction of SWCNT-aminopolymer composites with polar solvent vapours to obtain fast recovery and fast response is a significant advancement in gaining insights for the room-temperature gas detection with carbon-based materials.

Detection of ultra-low levels of DNA changes by drinking water: epidemiologically important finding.

The safety of drinking water is essential to our health. In this context, the mutagenicity of water needs to be checked strictly. However, from the methodological limit, the lower concentration (less than parts per million) of mutagenicity could not be detected, though there have been of interest in the effect of less concentration mutagens. Here, we describe a highly sensitive mutation assay that detects mutagens at the ppb level, termed genome profiling-based mutation assay (GPMA). This consists of two steps; (i) Escherichia coli culture in the medium with/without mutagens and (ii) Genome profiling (GP) method (an integrated method of random PCR, temperature gradient gel electrophoresis and computer-aided normalization). Owing to high sensitivity of this method, very low concentration of mutagens in tap water could be directly detected without introducing burdensome concentration processes, enabling rapid measurement of low concentration samples. Less expectedly, all of the tap waters tested (22 samples) were shown to be significantly mutagenic while mineral waters were not. Resultantly, this article informs two facts that the GPMA method is competent to measure the mutagenicity of waters directly and the experimental results supported the former reports that the city tap waters contain very low level of mutagenicity reagent trihalomethanes.

A plasmonic mercury sensor based on silver–gold alloy nanoparticles electrodeposited on indium tin oxide glass

We construct silver–gold alloy nanoparticles (Ag–AuNPs) as the basis of a reagentless, sensitive and simple mercury sensor. Ag–AuNPs were electrodeposited directly on transparent indium tin oxide film coated glass. Hg(II) ions in aqueous solution could be reduced by Ag atoms existing in Ag–AuNPs; the deposition/amalgamation of Hg on the nanoparticles resulted in a blue shift of the localized surface plasmon resonance peak. Therefore, Hg2+ can be detected quantitatively by using a spectrophotometer. The sensor response is linear in the range from 0.05 to 500ppb of Hg(II) concentration. No sample separation or preconcentration is required for detection of ultralow levels of mercury in water samples. The results shown herein have potential applications in the development of a new optical sensor for the detection of low concentrations of mercury.

Development of a surface plasmon assisted label-free calorimetric method for sensitive detection of mercury based on functionalized gold nanorods

In this investigation, we established a new sensitive, selective and label free optical method for the detection of mercury ions (Hg2+) by utilizing cyano (–CN) ligand functionalized gold nanorods (GNRs) based on the surface plasmon resonance (SPR) of the GNRs. The functionalization of the GNRs was specifically done with a –CN group containing polymer, poly(2-aminobenzonitrile) (P2ABN), to preconcentrate the Hg2+ ions on the surface of the GNRs prior to detection. The functionalization of the GNRs was carried out by two approaches. In the first approach, the GNR surface was modified with a porous silica network containing P2ABN (designated as GNR@silica-CN). In the second approach, GNR was modified with P2ABN (designated as GNR@P2ABN). The Hg2+ ion detection strategy involves the preconcentration of Hg ions on the surface of GNR@silica-CN or GNR@P2ABN through the interaction of the –CN groups in P2ABN with Hg2+ ions, reduction to Hg0 atoms by ascorbic acid (AA), and monitoring the SPR of GNRs. The porous network in GNR@silica-CN allows efficient migration of Hg0 to reach the GNR surface and causes effective amalgamation compared to GNR@P2ABN. As a result, GNR@silica-CN exhibits a significant change in the SPR of GNRs over a wide dynamic concentration range (from 50 nM to 5 μM) for Hg2+ ions. The very low detection limit of 1 ppb with GNR@silica-CN for Hg2+ ions suggests its excellent potential for the monitoring and detection of ultra low levels of Hg. In addition, the GNR@silica-CN shows no sensitivity for other environmentally relevant metal ions which confirms the high specificity for Hg2+ ion detection in practical samples. We demonstrated the effectiveness of the present method by detecting Hg2+ ions in spiked water (pond and water) samples. We envisage that this simple, fast and sensitive method will be suitable for environmental monitoring in the future.

Gold nanorods as surface enhanced Raman spectroscopy substrates for sensitive and selective detection of ultra-low levels of dithiocarbamate pesticides

We report the use of gold nanorods as solution-based SERS substrates for the detection of ultralow-levels of three different dithiocarbamate fungicides: thiram, ferbam and ziram. Gold nanorods are attractive to use as SERS substrates due to the ability to tune the surface plasmon resonance of the nanoparticles to the laser excitation wavelength of the Raman spectrometer equipped with a 785 nm diode laser. The gold nanorods are synthesized using a seed-mediated growth method and characterized using UV-Visible spectroscopy, zeta potential, and TEM. The gold nanorods have an aspect ratio of 2.19 ± 0.21 and have an average length of 37.81 ± 4.83 nm. SERS spectra are acquired at different concentrations of each fungicide and calibration curves are obtained by monitoring the intensity of the band arising from the ν(C-N) stretching mode coupled to the symmetric δ(CH(3)) motion. The limits of detection and limits of quantitation are obtained for each fungicide. The limits of detection are 11.00 ± 0.95 nM, 8.00 ± 1.01 nM, and 4.20 ± 1.22 nM for thiram, ferbam, and ziram respectively. The limits of quantitation are 34.43 ± 0.95 nM, 25.61 ± 1.01 nM, and 12.94 ± 1.22 nM for thiram, ferbam, and ziram respectively. It can be seen that the three different dithiocarbamates can be detected in the low nM range based on the limits of detection that are achieved.

Solution-based direct readout surface enhanced Raman spectroscopic (SERS) detection of ultra-low levels of thiram with dogbone shaped gold nanoparticles

We report the use of two different sizes of dogbone shaped gold nanoparticles as colloidal substrates for surface enhanced Raman spectroscopy (SERS) based detection of ultra-low levels of thiram, a dithiocarbamate fungicide. We demonstrate the ability to use a solution based, direct readout SERS method as a quantitative tool for the detection of ultra-low levels of thiram. The two different sizes of dogbone shaped gold nanoparticles are synthesized by using the seed-mediated growth method and characterized by using UV-visible spectroscopy and transmission electron microscopy (TEM). The smaller dogbone shaped nanoparticles have an average size of 43 ± 13 nm. The larger dogbone shaped gold nanoparticles have an average size of 65 ± 15 nm. The nanoparticle concentration is 1.25 × 10(11) nanoparticles per mL for the smaller dogbone shaped gold nanoparticles and is 1.13 × 10(11) nanoparticles per mL for the larger dogbone shaped gold nanoparticles. Different concentrations of thiram are allowed to bind to the two different sizes of dogbone shaped gold nanoparticles and the SERS spectra are obtained. From the calibration curve, the limit of detection for thiram is 43.9 ± 6.2 nM when the smaller dogbone shaped gold nanoparticles are used as colloidal SERS substrates In the case of the larger dogbone shaped gold nanoparticles, the limit of detection for thiram is 11.8 ± 3.2 nM. The lower limit of detection obtained by using the larger dogbone shaped gold nanoparticles as colloidal substrates is due to the lightning rod effect, higher contributions from the electromagnetic enhancement effect, and larger number of surface sites for thiram to bind.

Detection of ultra-low levels of pathologic prion protein in scrapie infected hamster brain homogenates using real-time immuno-PCR

Pathologic prion protein (PrP Sc), implicated in transmissible spongiform encephalopathies, is detected by antibody-based tests or bioassays to confirm the diagnosis of prion diseases. Presently, the Western blot or an ELISA is officially used to screen the brain stem in cattle for the presence of PrP Sc. The immuno-polymerase chain reaction (IPCR), a technique whereby the exponential amplification ability of PCR is coupled to the detection of proteins by antibodies in an ELISA format, was applied in a modified real-time IPCR method to detect ultra-low levels of prion protein. Using IPCR, recombinant hamster PrP C was consistently detected at 1 fg/mL and proteinase K (PK)-digested scrapie infected hamster brain homogenates diluted to 10 −8 (approximately 10–100 infectious units) was detected with a semi-quantitative dose response. This level of detection is 1 million-fold more sensitive than the levels detected by Western blot or ELISA and poises IPCR as a method capable of detecting PrP Sc in the pre-clinical phase of infection. Further, the data indicate that unless complete PK digestion of PrP C in biological materials is verified, ultrasensitive assays such as IPCR may inaccurately classify a sample as positive.

Accelerator Mass Spectrometry for the Detection of Ultra-Low Levels of Plutonium in Urine, Including That Excreted after the Ingestion of Irish Sea Sediments

Currently, most methods for the quantitative assessment of (239)Pu have minimum detection levels (25 microBq for alpha-particle spectrometry) that are much higher than the levels of this isotope in many human bioassay and environmental samples. Accordingly, a priority has existed to develop methods that are more sensitive. Fission-track and ICP-MS methods have been used, but these can suffer either from an uncertain level of removal and/or recovery of uranium or from isobaric mass interferences. Accelerator mass spectrometry (AMS) has no such disadvantages, and its demonstrated detection limits for plutonium isotopes approach levels of attograms, equivalent to about 500 nBq for (239)Pu. This paper describes the application of AMS to the measurement of (239)Pu in urine produced by youths living in London (3.5 microBq day(-1)) and by adults (approximately 2-260 microBq day(-1)), some of whom were exposed occupationally. In addition, an experiment was undertaken to measure the fasted absorbed fraction of ingested plutonium after the ingestion of 15 g of Irish Sea sediment by a volunteer. The measured absorbed fraction was 4.5 x 10(-5). It is concluded that accelerator mass spectrometry is a suitable method for the ultra-trace detection of plutonium.