Magnitude Improvement In Detection Limit Research Articles

High-Q asymmetrically cladded silicon nitride 1D photonic crystals cavities and hybrid external cavity lasers for sensing in air and liquids.

In this paper we show a novel design of high Q-factor silicon nitride (SiN) 1D photonic crystal (PhC) cavities side-coupled to curved waveguides, operating with both silica and air cladding. The engineering of the etched 1D PhC cavity sidewalls angle allows for high Q-factors over a wide range of upper cladding compositions, and the achievement of the highest calculated Q-factor for non-suspended asymmetric SiN PhC structures. We show the employment of these type of SiN PhC cavities in hybrid external cavity laser (HECL) configuration, with mode-hop free single mode laser operation over a broad range of injected currents (from 25 mA to 65 mA), milliwatts of power output (up to 9 mW) and side-mode suppression ratios in the range of 40 dB. We demonstrate the operation of these devices as compact and energy efficient optical sensors that respond to refractive index changes in the surrounding medium the measurement of sodium chloride (from 0% to 25%) and sucrose (from 0% to 25%) in aqueous solution. In HECL configuration, the RI sensor exhibits a 2 orders of magnitude improvement in detection limit compared to the passive microcavity. We also discuss the possibility for applying these devices as novel transducers for refractive index changes that are induced by analyte specific absorption of infrared radiation by the target analytes present in gas or liquid phase.

Iodide Functionalized Paper-Based SERS Sensors for Improved Detection of Narcotics.

An inkjet-printed paper-based Surface-enhanced Raman scattering (SERS) sensor is a robust and versatile device that provides trace sensing capabilities for the detection and analysis of narcotics and drugs. Such sensors generally work well for analytes with good binding affinity towards the Au or Ag plasmonic nanoparticles (NPs) resident in the sensors. In this report, we show that iodide functionalization of the printed sensors helps to remove adsorbed contaminants from AuNP surfaces enabling superior performance with improved detection of narcotics such as fentanyl, heroin and cocaine by SERS. SERS signals are easily doubled with the iodide-functionalized sensors which also showed orders of magnitude improvement in detection limit. In this report, we show that a short (90 s) iodide treatment of the sensors significantly improved the detection of heroin. We propose that iodide functionalization be integrated into field detection kits through the solvent that wets paper-based sensor prior to swabbing for narcotics. Alternatively, we have also demonstrated that iodide functionalized sensors can be stored in ambient for up to 1 week and retain the improved performance towards heroin detection. This report will help to significantly improve the performance of paper-based sensors for field detection of narcotic drugs.

Chemical stabilization of dispersed Escherichia coli for enhanced recovery with a handheld electroflotation system and detection by Loop-mediated Isothermal AMPlification.

Constraints related to sample preparation are some of the primary obstacles to widespread deployment of molecular diagnostics for rapid detection of trace quantities (≤103 CFU/mL) of food-borne pathogens. In this research, we report a sample preparation method using a novel handheld electroflotation system to concentrate and recover dilute quantities (102−103 CFU/mL) of Escherichia coli (E. coli) 25922 in artificially contaminated samples for reliable, rapid detection by loop-mediated isothermal amplification (LAMP). To protect suspended cells from shear stresses at bubble surfaces, a non-ionic surfactant (Pluronic-F68) and flocculant (chitosan oligosaccharide) were used to aggregate cells and reduce their surface hydrophobicity. Effective conditions for recovery were determined through multifactorial experiments including various concentrations of Pluronic-F68 (0.001, 0.01, 0.1, 1 g L-1), chitosan oligosaccharide (0.01, 0.1, 1, 10 g L-1), bacteria (102, 103, 104 CFU/mL E. coli 25922), recovery times (10, 15 and 20 minutes), and degrees of turbulent gas flux (“high” and “low”). The automated electroflotation system was capable of concentrating effectively all of the bacteria from a large sample (380 mL 0.1 M potassium phosphate buffer containing 102 CFU/mL E. coli) into a 1 mL recovered fraction in less than 30 minutes. This enabled detection of bacterial contaminants within 2 hours of collecting the sample, without a specialized laboratory facility or traditional enrichment methods, with at least a 2–3 order of magnitude improvement in detection limit compared to direct assay with LAMP.

Ultrasensitive Detection of Human Chorionic Gonadotropin Using Frequency Locked Microtoroid Optical Resonators.

Clean sport competition is of significant concern to many governments and sporting organizations. Highly sensitive and rapid sensors are needed to improve the detection of performance enhancing drugs in sports as athletes take diuretics to dilute the concentration of drugs in their urine and microdose under the detectable limits of current sensors. Here we demonstrate, using frequency locked microtoroid optical resonators, a 3 orders of magnitude improvement in detection limit over the current gold standard, mass spectrometry, for the common performance enhancing drug, human chorionic gonadotropin (hCG). hCG, also known as the pregnancy hormone, was detected both in simulated urine and in the urine of pregnant donors at a concentration of 1 and 3 femtomolar, respectively. We anticipate that the sensitivity provided by frequency locked optical microcavities can enable a new standard in antidoping research.

Catalytic hairpin assembly-programmed formation of clickable nucleic acids for electrochemical detection of liver cancer related short gene

DNA amplification usually takes place in an aqueous system to facilitate a highly efficient reaction. Therefore, it is a challenge to connect the DNA amplification with popular dry chemical methods, whose signal outputs usually come from a solid-liquid interface. Here, by linking catalytic hairpin assembly (CHA) with electrochemical biosensors through clickable nucleic acids, we develop a facile method for the detection of liver cancer related short gene MXR7. On one hand, the method maintains the advantages of CHA especially its high efficiency by performing the whole process of CHA in aqueous phase. On the other hand, the method realizes electrochemical detection of MXR7 by transferring a clickable double-helix production of MXR7-triggerd CHA to a dibenzocyclooctyne-functionalized electrode quickly through copper-free click chemistry. In comparison with traditional biotin-streptavidin or hybridization-assisted conjugation, the click chemistry allows quick response in a quarter of an hour, shortening the detection time greatly. In addition, owing to the lower steric hindrance as compared with streptavidin, the signal intensity is strong, making a sensitive detection possible. The detection limit reaches 125 fM, better than previous electrochemical methods. Results also reveal that CHA in solution has much better efficiency than that on interface, allowing two orders of magnitude improvement in detection limit (125 fM vs. 50 pM) with a shorter detection time (135 min vs. 165 min). This work also provides a novel concept to connect aqueous amplification system with interfacial detection method for other bio-analysis.

Development of an Electrochemical Paper-Based Analytical Device for Trace Detection of Virus Particles

Viral pathogens are a serious health threat around the world, particularly in resource limited settings, where current sensing approaches are often insufficient and slow, compounding the spread and burden of these pathogens. Here, we describe a label-free, point-of-care approach toward detection of virus particles, based on a microfluidic paper-based analytical device with integrated microwire Au electrodes. The device is initially characterized through capturing of streptavidin modified nanoparticles by biotin-modified microwires. An order of magnitude improvement in detection limits is achieved through use of a microfluidic device over a classical static paper-based device, due to enhanced mass transport and capturing of particles on the modified electrodes. Electrochemical impedance spectroscopy detection of West Nile virus particles was carried out using antibody functionalized Au microwires, achieving a detection limit of 10.2 particles in 50 μL of cell culture media. No increase in signal is found on addition of an excess of a nonspecific target (Sindbis). This detection motif is significantly cheaper (∼$1 per test) and faster (∼30 min) than current methods, while achieving the desired selectivity and sensitivity. This sensing motif represents a general platform for trace detection of a wide range of biological pathogens.

Improvement in detection limit for time-of-flight SIMS analysis of dopants in GaN structures

Secondary ion mass spectrometry (SIMS) has been used extensively to monitor dopant levels in semiconductor materials. The preponderance of these measurements has been made with magnetic sector or quadrupole analyzers. Use of time-of-flight (ToF) analyzers has been limited because of an inability to match the detection limit of the other analyzers. Optimization of the ToF-SIMS analysis beam pulse width and analysis frames per cycle is shown to provide as much as an order of magnitude improvement in detection limit. The magnesium dopant in GaN structures was used for the study and analysis was made with Cs+ sputtering source and Bi3+. The count rate for CsMg+ increased by a factor of 11.3 with both improvements applied. This was evidenced by a detection limit improvement for magnesium from 7.5 × 1017 atoms/cm3 to low 1017 atoms/cm3. Increasing the number of analysis frames from one to ten causes cycle time to increase by a factor of five. Hence, there is a tradeoff between improved detection limit and analysis time.

Reactive Charged Droplets for Reduction of Matrix Effects in Electrospray Ionization Mass Spectrometry.

A new quantitative contained-electrospray (ES) process is described here that employs a movable ES emitter to control the reactivity of charged microdroplets by varying their exposure time with acid vapor. The method allows elimination of ion suppression effects caused by the presence of various surface active compounds that coelute with the analyte. For mixtures, contained-ESI mass spectrometric analysis produces relative ion intensities that reflect the true concentrations of analytes in solution. The mechanism for this effect has been elucidated and ascribed to the generation of fine initial droplets in the presence of a high abundance of protons; together, these two factors eliminate competition for charge and space during ion formation. Examples of analytes tested include steroids, phospholipids, phosphopeptides, and sialylated glycans. At least 1 order of magnitude improvement in detection limits, sensitivity, and accuracy of detection was observed when compared to conventional electrospray.

A Pre-Concentrator for Explosive Vapor Detection

INTRODUCTION In recent years, the use of improvised explosive devices (IEDs) have become the preferred vehicle for terrorist attacks since they can be easily fabricated from readily available materials. This has raised concerns for the travelling public and prompted the need for a cost-effective, continuous monitoring system for explosives detection [1]. Recent works have been published regarding sensors and their ability to detect trace level explosives. Although these sensors address some of the needs for DHS, there is a limit to the modifications that can be made to these sensors in order to decrease the limit of detection. In this work, a pre-concentrator was developed as a means to increase the sensitivity of sensors used to detect vapor-phase explosives. Pre-concentrators employ sorbents that possess critical adsorption/desorption properties, thus allowing the delivery of a highly concentrated pulse of explosive vapor to the sensor. An order of magnitude improvement in detection limit was demonstrated for 2, 6-DNT and our pre-concentration approach shows considerable promise for the detection of other explosives at trace levels. EXPERIMENTAL Two microheaters were employed in our dynamically controlled sensor platform; one microheater was coated with a metal-oxide catalyst and a second microheater was left uncoated. The pre-concentrator, located upstream employed a spin-coated polystyrene film, which was deposited onto a third microheater, as shown in Figure 1. A carrier gas delivered the target molecules to the pre-concentrator for 180 seconds allowing time for collection of the explosive vapor. The pre-concentrator was then heated to desorb the explosive molecules, delivering a high concentration burst of 2, 6-DNT to both microheaters downstream. RESULTS Figure 2 illustrates the difference in signals after the thermal desorption of explosive molecules from the polymer. The response (signal) due to the pre-concentrator was nearly double that of the sensor alone. The results suggest an increase in power, signifying that an endothermic reaction occurs between the analyte and the catalyst. Figure 3 shows the detection limit obtained using the dual sensor (dynamically controlled) platform for TATP, which provides the baseline for comparison purposes; i.e. enhanced response due to pre-concentration. Further experiments were conducted to determine a gas flow that optimizes signal response, collection time and polymer film thickness and their role in the adsorption/desorption kinetics. CONCLUSION AND FUTURE WORK We have demonstrated that the addition of a polystyrene pre-concentrator to our sensor platform lowered the detection limit of 2, 6-DNT by an order of magnitude. Upon thermal desorption, there was an approximate 47% increase in sensor response. Future work will focus on developing other polymer pre-concentrators that will decrease the detection limit of other vapor phase explosives of interest. REFERENCES [1] Ras, M. R., F. Borrull, and R. M. Marcé. "Sampling and Preconcentration Techniques for Determination of Volatile Organic Compounds in Air Samples." TrAC Trends in Analytical Chemistry, 28.3 (2009): 347-61. Figure 1

The effect of pre-evaporation on ion distributions in inductively coupled plasma mass spectrometry

The connecting tube (2 or 5-mm i. d., 11-cm long) between the spray chamber and the torch was heated (to 400 °C) to investigate the effect of pre-evaporation on the distribution of ions in inductively coupled plasma mass spectrometry (ICP-MS). Axial and radial profiles of analyte ions (Al +, V +, Cr +, Ni +, Zn +, Mn +, Zn +, As +, Se +, Mo +, Cd +, Sb +, La +, Pb +) in 1% HNO 3 as well as some polyatomic ions (LaO +, ArO +, ArN +, CO 2 +) were simultaneously obtained on a time-of-flight ICP-MS instrument. Upon heating the connecting tube, the optimal axial position of all elements shifted closer to the load coil. Without the heated tube, 3.5 mm was the compromise axial position for multielemental analysis, which was optimal for 6 analytes. With the heated tube, this position became 1.5 mm, which was then optimal for 9 of the 14 analytes. Furthermore, the radial profiles, which were wide with a plateau in their middle without heating, became significantly narrower and Gaussian-like with a heated tube. This narrowing, which was most important for the 5-mm tube, slightly (by a factor of two at the most) yet significantly (at the 95% confidence level) improved the sensitivity of all elements but Mn upon optimisation of the axial position for compromise multi-element analysis. Furthermore, a concurrent decrease in the standard deviation of the blank was significant at the 95% confidence level for 9 of the 14 analytes. For most of the analytes, this translated into a two-fold to up to an order of magnitude improvement in detection limit, which is commensurate with a reduction of noise resulting from the smaller droplets entering the plasma after traversing the pre-evaporation tube.

Dual-Capillary Backscatter Interferometry for High-Sensitivity Nanoliter-Volume Refractive Index Detection with Density Gradient Compensation

A simple, stable, ultrasensitive dual-capillary dual-bicell (DCDB) microinterferometic backscattering detection (MIBD) system was developed. In DCDB MIBD, a He-Ne laser beam passes through a half-wave plate onto the cross section of two capillaries, one for reference and another for sensing analyte. The position of the backscattered fringe from each capillary, which are in proximity or essentially identical thermal environments, was detected with matched bicell photodetectors. The configuration was found to effectively compensate for thermal drift, which is normally the major source of noise in refractive index (RI) detection systems. It is shown that passive environmental compensation leads to greatly enhanced signal in nanoscale refractometry preformed by MIBD. An order of magnitude improvement in detection limits over single channel configurations is possible. Performance reaches the 10(-9) RIU level for like solvents in the presence in extremely large thermally induced RI gradients. At this level of detectability, DCDB MIBD could facilitate nanoliter-volume, femtomole-level universal detection in applications ranging from mu-HPLC and on-chip CE to scanning microcalorimetry.

Enhancing IR Detection Limits for Trace Polar Organics in Aqueous Solutions with Surface-Modified Sol-Gel-Coated ATR Sensors

An experimental investigation into the use of surface-modified sol-gel-coated Si attenuated total reflectance (ATR) mid-infrared sensors was completed to determine the detection limits for trace amounts of polar organic molecules in aqueous solutions. The surfaces of porous sol-gel films were modified to be mostly hydrophobic in order to concentrate the polar organic analytes in the film while largely excluding the water solvent. This modification of the Si ATR sensor coupled with multivariate partial least-squares calibration methods allowed approximately three orders of magnitude improvement in detection limits for acetone when compared to detection limits from univariate analysis of spectra obtained on uncoated Si ATR sensors. The comparable improvement for isopropanol in aqueous solution was over two orders of magnitude. Studies performed on mixtures of acetone and isopropanol in water confirmed that quantitative analyses could be performed on these mixture systems with cross-validated standard errors of prediction (CVSEP) of 0.5 and 8.7 ppm, respectively. Using three times the CVSEP as an estimate of the detection limit translates to detection limits of 1.5 and 26 ppm for acetone and isopropanol, respectively.

Enhanced sensitivity in laser ablation-ICP mass spectrometry using helium-argon mixtures as aerosol carrier

Laser ablation-ICP-MS is a sensitive and accurate technique for major to trace multi-element analysis at high spatial resolution on the scale of 10 µm. A wide variety of samples can be studied quantitatively, including minerals and their solid, liquid or melt inclusions as required for geochemical studies. As the desired spatial resolution increases, however, detection limits become severely constrained by the total amount of sample material reaching the ICP. Detection limits are therefore determined by the ablation rate and by the efficiency of removal of ablated aerosol particles from the ablation spot and their transport into the plasma. Properties of the carrier gas are known to affect the ablation process and the efficiency of particle transportation. This study explores the effects of different ablation-cell configurations and the use of helium, dry argon and argon moistened with water for the transport of aerosols into an ICP-MS, using a prototype 193 nm ArF excimer laser. Deposition of visible particles deposited around the ablation pit is significantly reduced when helium is used instead of argon. A moderate flux of helium through the chamber, mixed with moistened argon immediately downstream from the ablation chamber, leads to at least a 2-3-fold increase in the signal intensities across the entire mass range when compared with argon gas only. Background intensities above mass 85 are significantly reduced, but polyatomic interferences in the low mass region increase by an order of magnitude, owing to oxide formation caused by the water load. A high flux of helium, mixed just behind the ablation cell with dry argon, yields a 2-3-fold sensitivity enhancement, in addition to greatly reduced background intensity across the entire mass range. This results in one order of magnitude improvement in detection limits for most elements. These modifications permit the routine determination of minor concentrations of chlorine in microscopic fluid inclusions or the analysis of minerals, such as trace element concentrations in quartz (e.g., Na and Li down to 500 ng g –1 , using a 40 µ ablation pit). Furthermore, this improved sensitivity has recently yielded the first quantitative determination of gold concentrations (∼0.1 µg g –1 ) and full rare-earth element patterns in single 25 µm fluid inclusions.

Total reflection x-ray fluorescence spectroscopy using synchrotron radiation for wafer surface trace impurity analysis (invited)

Trace impurity analysis is essential for the development of competitive silicon circuit technologies. Current best methods for chemically identifying and quantifying surface and near-surface impurities include grazing incidence x-ray fluorescence techniques using rotating anode x-ray sources. To date, this method falls short of what is needed for future process generations. However, the work described here demonstrates that with the use of synchrotron radiation, total reflection x-ray fluorescence methods can be extended to meet projected needs of the silicon circuit industry until, at least, the year 2000. The present results represent over an order of magnitude improvement in detection limit over what has been reported previously. A double multilayer monochromator on a high flux wiggler beam line resulted in a detection limit for Ni of 3×108 atoms/cm2. This is to be compared with a detection limit of 5×109 atoms/cm2 obtained with a rotating anode system. This is due to the greatly improved signal to background in the case of the synchrotron. Furthermore, there is a path to improving the synchrotron case to reach a detection limit of 5×107 atoms/cm2.

Application of sample stacking to gravity injection in capillary electrophoresis

AbstractSample stacking can be used to increase the amount of analyte loaded onto a capillary column without loss in resolution. After the sample is loaded onto the column, the analytes are then separated by conventional capillary zone electrophoresis. When using gravity injection, over an order of magnitude improvement in detection limit is achieved. There is an optimal point for the amount of material which can be injected onto the column based on the resolution desired for the separation.

Ultramicroelectrode ensembles. Comparison of experimental and theoretical responses and evaluation of electroanalytical detection limits

Abstract : The ultramicroelectrode ensembles yield responses which are in quantitative agreement with predictions of established electrochemical theory. Furthermore, a one order of magnitude improvement in detection limits (relative to a conventional, macro-sized electrode) is demonstrated. In a recent correspondence, we described a new procedure for preparing ultramicrodisk electrode ensembles; the ultramicrodisks were formed by filling the pores of a microporous host menbrane with carbon paste. In this paper we present results of quantitative and semi-quantitative analyses of the electrochemical response characteristics of these ultramicroelectrode ensembles; we show that the responses are in agreement with predictions of established electrochemical theory. We also show that one of the ensembles investigated here can yield electroanalytical detection limits which are order of a magnitude lower than detection limits at an equivalent macro-sized (0.331 sq.cm.) electrode. Ultramicrodisk electrode, Electrochemical response, Electroanalytical detection limits.