IGZO-Based Simple, Scalable, and Linear Response Semitransparent Sensors for Sub-ppm NO₂ Detection

One of the top design priorities for gas sensors is developing simple, low-cost, sensitive and reliable sensors to be built in handheld portable devices. The present paper deals with the fabrication technique and sensing mechanism of a novel room temperature sensor for detection and quantification of highly inflammable Liquefied Petroleum Gas (LPG) and Carbon monoxide gas at room temperature. The detection of the presence of LPG and CO gas is based on the fact that the resistance of the sensing material of the device changes drastically when exposed to LPG and CO uniquely. This sensor is highly sensitive, repeatable, cost effective, portable, flexible and water proof; very less response as well as degassing time, simple fabrication technique, requires no extra dopants and can easily measure the leakage of LPG and CO as low as 80 ppm at ambient conditions. The fabricated graphite film sensors for the detection of LPG and CO gas have several advantages over conventional metal oxide sensors such as reduced size, low power consumption, room temperature operation and flexibility.

Several simple sensors were fabricated through a one-step method. By depositing electro-active compounds, such as β-cyclodextrins (β-CD), heme, dopamine (DA), or Fc-ECG, onto a screen-printed electrode (SPE), the successful simultaneous detection of nitrite (NO2−) and thiosulfate (S2O32−) ions was observed. Under optimal operating conditions, the notable electrocatalytic abilities of a Heme/SPE sensor were detected for the oxidation of NO2− and S2O32−, with remarkable peak potential differences, after characterization via SEM, CV, and DPV. Linear relationships were obtained in the ranges of 5.0–200.0 μmol L−1 and 1.0–100.0 μmol L−1 for the current response versus concentration of NO2− and S2O32−, respectively. The limits of detection were determined to be 1.67 and 0.33 μmol L−1 while the sensitivities of detection were noted to be 0.43 and 1.43 μA μM−1 cm−2, respectively. During the detection of NO2− and S2O32−, no interfering common ions were observed. Furthermore, average recoveries from 96.0 to 104.3% and a total R.S.D. of less than 3.1% were found for the detection of NO2− and S2O32− in pickled juice and tap water using the simple sensor. These results showed that rapid and precise measurements for actual application in NO2− and S2O32− detection could be conducted in food samples, indicating a potential use in food safety.

The development of a simple sensor (9NL27-Zn) based on DNAzyme and PCR and aimed at the detection of low concentrations of zinc (II) ions is described. A specific Zn(II)-dependent DNAzyme (9NL27) with DNA-cleaving activity was employed. In the presence of zinc (II), the DNAzyme hydrolyzed DNA substrate into two pieces (5' and 3' fragments), forming 3'-terminal hydroxyl in the 5' fragment and 5'-phosphate in the 3' fragments. Subsequently, the 5' fragment left the DNAzyme and bound a short DNA template. The 5' fragment was used as a primer and extended a single-stranded full-length template by Taq polymerase. Finally, this full-length template was amplified by PCR. The amplified products had a quantitative relationship with Zn(II) concentration. Under our experimental conditions, the DNA sensor showed sensitivity (10 nM) and high specificity for zinc ion detection. After improvement of the DNA sensor, the detection limit can reach 1 nM. The simple DNA sensor may become a DNA model for the detection of trace amounts of other targets.

A smartphone-based fluorescent sensor for rapid detection of multiple pathogenic bacteria

Enhanced near-infrared QEPAS sensor for sub-ppm level H2S detection by means of a fiber amplified 1582 nm DFB laser

Chemoresistive Gas Sensors for Sub-ppm Acetone Detection

In this work, we report a simple but efficient voltammetric sensor for simultaneous detection of ponceau 4R and tartrazine based on TiO2/electro-reduced graphene oxide nanocomposites (TiO2/ErGO). TiO2/ErGO nanocomposites were prepared by ultrasonically dispersing TiO2 nanoparticles (TiO2 NPs) into graphene oxide (GO) solution followed by a green in-situ electrochemical reduction. TiO2 NPs were uniformly supported on ErGO nanoflakes, which provides a favorable interface for the adsorption and subsequent oxidation of target analytes. TiO2/ErGO showed remarkable electrocatalytic capacity for the oxidation of ponceau 4R and tartrazine, with minimized oxidation overpotentials and boosted adsorptive striping differential pulse voltammetric (AdSDPV) response peak currents. Under the optimal experimental conditions, the anodic peak currents of ponceau 4R and tartrazine increase linearly with the respective natural logarithm of concentrations from 0.01 to 5.0 μM. The detection limits (LOD = 3σ/s) for ponceau 4R and tartrazine are 4.0 and 6.0 nM, respectively. The extraordinary analytical properties of TiO2/ErGO/GCE are primarily attributed to the synergistic enhancement effect from ErGO nanoflakes and TiO2 NPs. Moreover, the proposed TiO2/ErGO/GCE achieves reliable determination of ponceau 4R and tartrazine in orange juice with excellent selectively, reproducibility and stability. Together with simplicity, rapidness, and low cost, the proposed sensor demonstrates great potential for on-site detection of azo colorants.

The intrinsic fluorescence of berberine is very weak, which can be enhanced by its interaction with specific aptamers. A simple and sensitive DNA sensor for visual detection of berberine has here been established. When using this sensor, there was a good linear relationship between the change in fluorescence intensity of berberine and the concentration of berberine in the range of 16-2000 nM, with a detection limit of 5.1 nM. The change in fluorescence intensity was caused by the addition of aptamers. A detection limit of 170.1 nM was acquired by reading the RGB values of fluorescent images with a smartphone for the quantification of berberine. Common antibiotics did not interfere with the measurement of the berberine concentration. The molecular ion peaks of the complexes formed by the aptamer and berberine could be clearly observed by electrospray ionization mass spectrometry. The UV-vis absorption spectra, circular dichroism spectra, and fluorescence spectra indicated a strong interaction between berberine and the aptamer. The dissociation constant (Kd) between berberine and the aptamer was 1.91 μM. This sensor was both simple and sensitive, requiring only a 21-base oligonucleotide. It realized a visual quantitative analysis with a smartphone. This method could also be used for similar fluorescence visualization determination of aptamer-based drug molecules.

A simple, inexpensive and fast colorimetric method was developed for the detection of hydralazine, which is an antihypertensive drug. The method is based on the reaction of HY with ferric ions (as oxidizing agent) in the presence of ferricyanide ion and formation of prussian blue nanoparticles (KFeIII[FeII(CN)6]). A UV-vis spectrophotometer was used to monitor the changes of the absorption intensity of the prussian blue nanoparticles. These nanoparticles exhibited a strong UV-vis extinction band at 700 nm. Change in color of the solution, which is directly related to the HY concentration, could be easily observed with the naked eye in the presence of a sub-ppm level of HY. The effect of several reaction variables on the rate of the PBNP formation was studied and optimized. A linear relationship between absorbance intensity of PBNPs and the concentration of HY over a range of 0.4 μg mL−1 to 2.0 μg mL−1 with correlation coefficient (R2) of 0.9967 was observed; moreover, the detection limit was found to be 0.33 μg mL−1. The proposed method showed a good detection limit, and compared to other methods it is very fast, simple and inexpensive. Furthermore, the proposed method was successfully applied for the determination of HY concentration in pharmaceutical samples with satisfactory results.

We developed inexpensive and disposable gas sensors with a low environmental footprint. This approach is based on a biodegradable substrate, paper, and features safe and nontoxic electronic materials. We show that abrasion-induced deposited WS2 nanoplatelets on paper can be employed as a successful sensing layer to develop high-sensitivity and selective sensors, which operate even at room temperature. Its performance is investigated, at room temperature, against NO2 exposure, finding that the electrical resistance of the device drops dramatically upon NO2 adsorption, decreasing by ~42% (~31% half a year later) for 0.8 ppm concentration, and establishing a detection limit around~2 ppb (~3 ppb half a year later). The sensor is highly selective towards NO2 gas with respect to the interferents NH3 and CO, whose responses were only 1.8% (obtained for 30 ppm) and 1.5% (obtained for 8 ppm), respectively. Interestingly, an improved response of the developed sensor under humid conditions was observed (tested for 25% relative humidity at 23 °C). The high-performance, in conjunction with its small dimensions, low cost, operation at room temperature, and the possibility of using it as a portable system, makes this sensor a promising candidate for continuous monitoring of NO2 on-site.

Novel Bi2S3/Bi2O3 hybrid materials with unique mesoporous structures were successfully synthesized via a facile in situ elevated-temperature thermal oxidation method using the Bi2S3 as a precursor in air. The as-prepared Bi2S3/Bi2O3 heterostructure-based sensor exhibits an excellent performance for detecting sub-ppm concentrations of NO2 at room temperature (RT). In the presence of 8 ppm NO2, the sensor registers a response of approximately 7.85, reflecting a 3.5-fold increase compared to the pristine Bi2S3-based sensor. The response time is 71 s, while the recovery time is 238 s, which are reduced by 32.4% and 24.2%, respectively, compared to the pristine Bi2S3-based sensor. The Bi2S3/Bi2O3 heterostructure-based sensor achieves an impressively low detection limit of 0.1 ppm for NO2, and the sensor has been demonstrated to possess superior signal repeatability, gas selectivity, and long-term stability. The optimal preparation conditions of the hybrid materials were explored, and the formation of mesoporous structure was analyzed. The obviously improved gas sensitivity of the Bi2S3/Bi2O3 heterostructure-based sensor can be assigned to the combined influence of electronic sensitization and its distinctive morphological structure. The potential gas-sensitive mechanisms were revealed by employing density functional theory (DFT). It was found that the formation of heterostructures could enhance the adsorption energies and increase the amount of electron transfer between NO2 molecules and the hybrid materials. Furthermore, the electron redistribution driven by orbital hybridization between O and Bi atoms improves the capacity of NO2 molecules to capture additional electrons from the Bi2S3/Bi2O3 heterostructures. The content of this work supplies an innovative design strategy for constructing NO2 sensor with high performance and low energy consumption at RT.

A simple microwave sensor for the detection of the dynamic characteristics of large structure vibration is proposed. It consists of a continuous-wave radar capable of detecting the structure movement by measuring the phase of the back-reflected wave. The system performances have been demonstrated in a case study monitoring a pedestrian bridge.

Non-aromatic single amino acid, lysine: A simple fluorescence sensor for selective detection of Cu2+ and Co2+ with colorimetric distinction by the virtue of its self-aggregation behaviour

New hybrid materials – photosensitized nanocomposites containing nanocrystal heterostructures with spatial charge separation, show high response for practically important sub-ppm level NO2 detection at room temperature. Nanocomposites ZnO/CdSe, ZnO/(CdS@CdSe), ZnO/(ZnSe@CdS) were obtained by the immobilization of nanocrystals – colloidal quantum dots (QDs), on the matrix of nanocrystalline ZnO. The formation of crystalline core-shell structure of QDs was confirmed by HAADF-STEM coupled with EELS mapping. Optical properties of photosensitizers have been investigated by optical absorption and luminescence spectroscopy combined with spectral dependences of photoconductivity, which proved different charge localization regimes. Photoelectrical and gas sensor properties of nanocomposites have been studied at room temperature under green light (λmax = 535 nm) illumination in the presence of 0.12 – 2 ppm NO2 in air. It has been demonstrated that sensitization with type II heterostructure ZnSe@CdS with staggered gap provides the rapid growth of effective photoresponse with the increase in the NO2 concentration in air and the highest sensor sensitivity toward NO2. We believe that the use of core-shell QDs with spatial charge separation opens new possibilities in the development of light-activated gas sensors working without thermal heating.

Introduction Naloxone, (5α)-4,5-epoxy,3,14-dihydroxy17(2-propenyl) morphinan-6-one, (Figure 1) is a synthetic opioid receptor antagonist mainly used for the treatment of opioid overdose and to reduce constipation caused by orally administered opioid therapy [1]. A number of analytical methods have been reported for the detection of naloxone, mainly by high performance liquid chromatography [2], high performance liquid chromatography coupled with mass spectrometry [3] and chemiluminescence [4]. However, the methods are costly, time consuming, produce large amounts of liquid waste which is not environment friendly, and not appropriate for field use. Electrochemical sensor platforms, however, are attractive for handheld detection and field use due to their low sample volume requirement, simplicity and compactness. In this work, we report on the development of simple, yet sensitive and selective electrochemical sensor for naloxone detection using molecular imprinted polymer (MIP) and screen printing electrodes. Method The MIP preparation was carried out via in situ electropolymerization of a solution composed of the functional monomer, p-phenylenediamine (pPD), and the template (naloxone) in phosphate citrate buffer at pH 6 on a screen printed carbon electrode that was modified with reduced graphene oxide (rGO) and gold nanoparticle (AuNPs) (Figure 2). Several parameters controlling the preparation and performance of the MIP sensor (including pH, the molar ratio between monomer and template molecules, the cycle number of electropolymerization, and incubation time of the modified electrode on the sensing performance) were studied and optimized. After electropolymerization, naloxone molecules were removed from the MIP using methanol/HCl solution to generate binding sites that were complimentary in size, shape and functionality to naloxone molecules for later detection. Non-imprinted polymer (NIP) modified electrodes were prepared using the optimized procedure but in the absence of naloxone to examine the selectivity of the MIP sensor. The electrochemical behavior of naloxone at MIP and NIP sensors was evaluated by differential pulse voltammetry. Results and Conclusions The morphology and properties of the sensing material were characterized with scanning electron microscopy, Raman spectroscopy, and atomic force microscope. Under an optimized condition, the MIP electrochemical sensor responded linearly to naloxone concentration between 0.5 μM to 8 μM, with a detection limit of 0.23 μM. The introduction of rGO and AuNPs hybrid materials significantly improved the sensor’s performance. The selectivity of the MIP sensor towards naloxone was examined using morphine, naltrexone and noroxymorphone as interferents. The result of the selectivity experiment showed that the imprinted electrode has a good response and selectivity towards naloxone. To further demonstrate the potential of the developed MIP-based naloxone sensor for practical applications, the sensor was tested for the detection of naloxone in spiked urine samples. Recoveries of up to 97.0% were recorded, demonstrating the reliability and accuracy of the sensor for naloxone detection in bodily fluids.