Naked-eye Detection Research Articles

Photonic crystal sensor for melamine based on magnetic molecularly imprinted nanoparticles self-assembled with an amphiphilic random copolymer.

Magnetic molecularly imprinted nanoparticles (MMINPs) were obtained with a one-step process through miniemulsion self-assembly using an amphiphilic random copolymer as both an emulsifier and MMINP coating, oleic acid-modified magnetite nanoparticles as magnetic cores, and melamine (MEL) as the template molecule. MMINPs were assembled under an external magnetic field to construct photonic crystal (PC) sensor for naked-eye detection of MEL. The MMINPs were characterized by FT-IR, TEM, TGA, and VSM. The analytical performances of themagnetic molecularly imprinted PC sensor for MEL (MEL-MMIPCs) were investigated with respect to sensitivity, response time, selectivity, and stability. As the MEL concentration increases from 1.0 to 1.0 × 106μg/l, the reflection wavelength of MEL-MMIPCs shifted from 497 to 709nm, and was linear with the logarithm of MEL concentration in this range. The detection limit was 0.21μg/l (S/N = 3) and response time was within 30s. The MEL-MMIPC sensor had an imprinting factor of 5.09, and selectivity factors for theanalogs cyanuric acid and atrazine were 8.76 and 5.75, respectively, indicating the high sensitivity and selectivity. After 10 cycles of elution/response, MEL-MMIPCs still had a good ability to recognize MEL.

Semiquantitative naked-eye detection of synthetic food colorants using highly-branched pipette tip as an all-in-one device

The existing strategies for the determination of synthetic food colorants (FCs) in manufactured foods are highly relied on specialized instruments and skilled personnel which are limited by the high technical threshold and instrumentation cost. Herein, highly branched pipette tips (PTs) were fabricated as a robust all-in-one device for high-performance extraction and visual detection of FCs via handy aspiration and dispensing procedures of pipette controller. The density of extraction groups and inner specific surface area of PTs greatly increased after facile physical coating and subsequent layer-by-layer branching reactions, and the maximum increment in binding capacity of PTs was exceeded 300 times at 8–10 iterations of branching layers, enabling the PTs to be colored just by short-time extraction of FCs and to achieve the instrument-independent visual detection of FCs by virtue of their outstanding PT-SPE performance. As a proof-of-concept, the in-situ PT-based solid phase extraction (PT-SPE) with high recoveries (from 91.73 ± 4.76% to 99.90 ± 4.14%) and semiquantitative naked-eye detection of FCs (Allura red and brilliant blue) in real beverages were experimentally demonstrated to be highly feasible by comparison with classical techniques like spectrophotometry, HPLC, and mass spectrometry.

Ratiometric photothermal detection of silver ions using diimmonium salts.

Selective detection and determination of silver ions are tricky due to the poor reactivity and the interference of various metal ions and halides. Only a few cases have been reported concerning sulfur-based functionality. This work proposes silver-selective probes exhibiting peculiar colorimetric and photothermal responses without the need for sulfur-functional groups. Tetrakis(4-dialklyaminophenyl)1,4-phenylenediamine containing hexyl and methoxytriethyleneglycol substituents, PTS1 and PTS2, respectively, are selectively oxidized by silver ions to form dicationic diimmonium salts. The resulting quinone diimminium salts show strong absorption in the near-infrared (NIR) region with intense color changes. The striking color change is observed from pale brown to intense olive green with immediate responses. PTS1 shows a higher binding constant and nanomolar detection limit, whereas PTS2 shows a sub-micromolar detection limit. Job's plot studies reveal the stoichiometric ratio as 1:2 (PTS1: Ag+). Due to the strong NIR absorption of the oxidized PTS probes, the temperature rise is monitored, after adding silver ions, by a thermal camera and in-contact thermal sensors. The concentration of the actual samples can be determined based on a calibration plot with a temperature change as a function of silver ion concentration. The current results offer highly selective and ultrasensitive probes for silver ions under multiple detection mediums, including naked eye and photothermal detection.

Development and evaluation of a real-time fluorescence, and naked-eye colorimetric, loop-mediated isothermal amplification-based method for the rapid detection of spoilage fungi in fruit preparations

DNA-based techniques like PCR/qPCR have been applied for the detection of microorganisms in order to provide faster results, due to their high sensitivity and specificity, when compared to culture-based techniques. However, isothermal amplification techniques like Loop-mediated isothermal amplification (LAMP) have emerged lately allowing the simplification of the assays, and reduction of costs. The aim of this study was the development, and evaluation, of a panfungal LAMP assay (LAMP- 18S) for the fast detection of spoilage fungi in fruit preparations. In this sense, a set of primers was newly designed. Two different detection strategies were examined, namely real-time fluorescence and naked-eye colour detection. In addition, the results were compared against another published panfungal LAMP (LAMP-POW) and a qPCR assay, which served as the reference method. The developed method showed high sensitivity being able to detect down to 1.4 pg/reaction for yeasts and 170 pg/reaction for moulds. The addition of an enrichment step significantly reduced the LOD as the method could reliably detect yeasts with a LOD95 of 3.1 and 3.0 CFU/50 g for the fluorescent and colorimetric assay, respectively. The fluorescent assay showed “substantial agreement” with the reference method, while the colorimetric assay was “almost in complete concordance” with the reference method. Overall, a reliable and sensitive next-day detection method for fungi was achieved.

Sensitive plasmonic ELISA assay based on butyrylcholinesterase catalyzed hydrolysis for the detection of Staphylococcus aureus

Enzyme-linked immunosorbent assay (ELISA) is one of the most powerful techniques for biomolecule detection, but suffers from insufficient sensitivity and relatively tedious operation. In this paper, we present a highly sensitive ELISA approach for Staphylococcus aureus (S. aureus) determination. S. aureus is first captured by vancomycin (Van) and butyrylcholinesterase (BChE) co-functionalized magnetic beads (MBs), and then immobilized on a 96-well plate through the binding with the precoated IgG. Afterwards, gold nanoparticles (AuNPs) and butyrylthiocholine (BTCh) are added, allowing BChE to catalyze BTCh into thiocholine (TCh). The presence of TCh triggers the aggregation of AuNPs, resulting in distinct color change from red to purple. Therefore, a sensitive quantification method for S. aureus can be developed based on the correlation between the amount of S. aureus and the color change of AuNPs. Under optimal conditions, naked eye detection can be realized at S. aureus down to 100 CFU mL−1. A limit of detection of 5 CFU mL−1 can be reached with microplate reader measurement, along with a dynamic range of 5–102 CFU mL−1 and 102-107 CFU mL−1. The system is selective towards S. aureus and shows resistance to other bacteria. By taking advantage of the high sensitivity of enzymatic reaction and AuNPs-based colorimetric method, this method greatly improves the dynamic range and sensitivity, providing alternative approach for the sensitive detection of S. aureus.

Colorimetric biosensor for the naked-eye detection of ovarian cancer biomarker PDGF using citrate modified gold nanoparticles

Ovarian cancer is one of the fatal diseases in women. However, it can be cured if the early-stage diagnosis and suitable treatment is given on time. The goal of the research is to produce nano-biosensing technology for early identification of fatal ovarian cancer. In this regard, a rapid and colorimetric nano-biosensor was constructed employing gold nanoparticles to target platelet-derived growth factor (PDGF), a circulating biomarker that is up-regulated in plasma in prevalent ovarian cancer. The findings were supported by spectroscopy analysis and characterized the nanoparticles using SEM (Scanning electron microscopy & XRD (X-ray diffraction). In this proposed principle, gold nanoparticles (AuNPs) are mixed with PDGF specific aptamer and employed to identify PDGF by screening changes in the color as well as absorbance of the Aptamer and AuNPs caused by aggregation. The AuNPs color changes from pinkish to light purple at higher level of concentration. Signal-output exhibited for PDGF was in the linear range of 0.01–10 μg/ml under the optimum conditions. The change in color of gold nanoparticles was seen when the concentration of PDGF was as low as 0.01 μg/ml. Also, the developed technique was successfully applied in artificial serum which have many components of biofluids. The results we presented in this research can imply the practical application of aptamer and AuNPs in cancer diagnosis, exhibiting its benefits of reliability, selectivity, and reproducibility.

A new spiropyran compound for selective naked-eye detection of copper ions in aqueous media and on test paper strips

Using a strategy of modifying a bis(pyridin-2-ylmethyl) amino group in the 5-position, a new spiropyran dye ((1′-ethyl-3′,3′-dimethyl-N, N-bis(pyridin-2-ylmethyl) was synthesized. The dye was able to distinguish copper ions with remarkable selectivity by naked eye on paper strips and in aqueous media. Copper ions are selectively coupled to the receptor, which stimulates the opening of the spirocycle. Consequently, the π -electrons are localized on the spiropyran and a new absorption peak appears between 450 and 600 nm. Due to its functional properties, the receptor facilitates the rapid, selective, and sensitive detection of copper ions with a detection limit of 19 nM. According to Job's plot analysis, the correlation ratio between the probe and copper ions appears to be 2:1. Further, the probe was successfully applied to test papers strips that demonstrated distinct colors changes in response to different concentrations of copper ions.

Smart MOF‐on‐MOF Hydrogel as a Simple Rod‐shaped Core for Visual Detection and Effective Removal of Pesticides

The immoderate use of pesticides in the modern agricultural industry has led to the pollution of water resources and ultimately threatens the human body. Herein, two metal-organic frameworks (MOFs), namely {[Zn(tpt)2 ·2H2 O]}n (Zn1) and {[Zn2 (tpt)2 (bdc)]}n (Zn2), (Htpt = 5-[4(1H-1,2,4-triazol-1-yl)]phenyl-2H-tetrazole), respectively, are constructed as smart materials for visual and on-site detection of pesticides and their removal from water. The exposed nitrogen-rich sites and high chemical stability make Zn2 a self-assembly core to further fabricate MOF-on-MOF-sodium alginate (ZIF-8-on-Zn2@SA) composite by wrapping ZIF-8 on the outside surface. Inheriting the excellent fluorescent emission of Zn2, the rod-like ZIF-8-on-Zn2@SA module exhibits naked-eye detection of thiophanate-methyl (TM) in real fruits and vegetables with a broad linear range (10-100×10-6 m), a low limit of detection (LOD = 0.14×10-6 m), and satisfactory recoveries (98.30-102.70%). In addition, carbendazim (CBZ), the metabolite of TM after usage in crops, can be efficiently removed from water by the ZIF-8-on-Zn2@SA (qmax = 161.8 mgg-1 ) with a high correlation coefficient (R2 >0.99). Therefore, the portable ZIF-8-on-Zn2@SA sensing platform presents a promising candidate for monitoring and removal of pesticides, especially suitable for regions with serious pesticide environmental pollution.

Green synthesis of phenolic capping Ag NPs by green walnut husk extract and its application for colorimetric detection of Cd2+ and Ni2+ ions in environmental samples

This study assessed the green synthesis of phenolic capping silver nanoparticles (PC-Ag NPs) using the green walnut husk (GWH) extract of Juglans regia (J. Regia) as reducing and stabilizing agents. The synthesized nanoparticles were evaluated in terms of optical and chemical properties. The results of the analysis confirmed that the PC-Ag NPs formed successfully. Next, the prepared nanoparticles were applied as a colorimetric sensor for spectra and naked-eye detection of Cd2+ and Ni2+ ions. Owing to the reaction of functional groups of GWH extract, including hydroxyl and carboxyl on the surface of detector nanoparticles with Cd2+ and Ni2+ ions, aggregation and sedimentation occurred. These reactions suggest the formation of chelate complexes through polyphenol capabilities to chelate metals. Under optimized conditions (pH = 6, reaction time = 75 min), the introduced nanosensor exhibited good selectivity, sensitivity, and linearity (with R2 = 0.9899 and 0.9922 for Cd2+ and Ni2+, respectively). The detection limit of the reported method was 0.2 nM. Further, the synthesized nanosensor was utilized to determine target analytes in environmental samples, whereby satisfactory recoveries were achieved within 90.57 to 113.61%.

A point-of-use lateral flow aptasensor for naked-eye detection of aflatoxin B1

Aflatoxin B1 (AFB1) contamination in food is not only a serious health threat to humans, but also a considerable economic burden worldwide. Rapid and accurate detection of AFB1 during production, processing, transportation and storage is therefore a prerequisite to prevent spreading of AFB1. Here, we developed a simple and easy-to-use lateral flow aptasensor (LFA) to visually detect AFB1 using AFB1 aptamer. Polystyrene dyed particles were used as a signal reporter to enable colorimetric readout by naked eyes, in which the signal is directly proportional to the concentration of AFB1. Both aptamer specificity and target induced strand release approach enable a single-step AFB1 detection. The whole assay took 35 min to complete, starting from sample/dye complex incubation to color acquisition. Under the optimized condition, this sensing platform could detect AFB1 as low as 4.56 ng mL−1 with two distinct linear ranges of 0–0.05 μg mL−1 and 0.05–1 μg mL−1. LFA validation with 4 spiked samples (peanut, corn, rice and chili powder) showed satisfying AFB1 recovery within the range of 90.83–110.21%. Our LFA platform could potentially be applied to the on-site, naked-eye, and instrument-free detection of AFB1 or other substances with available aptamers.

Detection of porcine DNA in food using direct asymmetric PCR and catalyzed hairpin assembly fluorescent biosensor: A novel assay for halal food analysis

Adulteration of halal-certified food with pork are often reported. Using direct PCR results in cost- and time-saving benefits, and allows flexibility in amplicon detection. Here, we aimed to develop and validate a novel, direct asymmetric PCR and catalyzed hairpin assembly fluorescent biosensor (daPCR-CHA-FB) with a portable LED lightbox for naked eye detection of porcine DNA in raw and processed food. We tested the assay's reproducibility, specificity, sensitivity, real-world applicability, and single-blind performance. Using only 1 mm3 samples, reproducibility test with 38 raw pork samples showed 2.6% false negative rate and 0.0% false positive rate. The lowest detection limits were 0.01 ng for porcine DNA and 0.1% for binary pork-and-beef mixture. No cross-reaction with 16 other species was observed. One-hundred market samples showed no false negative for pork-listed samples, while two samples declared as non-pork showed a positive reaction. The assay was simple, sensitive, specific, safe, and robust. It could be used by law enforcement agencies and small-scale laboratories to investigate contamination and adulteration of halal foods.

Rapid Assembly of Magnetoplasmonic Photonic Arrays for Brilliant, Noniridescent, and Stimuli-Responsive Structural Colors.

There are usually trade-offs between maximizing the color saturation and brightness and minimizing the angle-dependent effect in structural colors. Here, a magnetic field-induced assembly for the rapid formation of scalable, uniform amorphous photonic arrays (APAs) featuring unique structural colors is demonstrated. The magnetic field plays a fundamental role in photonic film formation, making this assembly technology versatile for developing structural color patterns on arbitrary substrates. The synergistic combination of surface plasmonic resonance of the Ag core and broadband light absorption of high refractive index (RI) Fe3 O4 shell in hybrid magnetoplasmonic nanoparticles (MagPlas NPs) enables breaking the trade-offs to produce brilliant, noniridescent structural colors with high tunability and responsiveness. These features enable the fabrication of various types of highly sensitive and reliable colorimetric sensors for naked-eye detection without sophisticated instruments. Furthermore, large-scale structural color patterns are effortlessly achieved, demonstrating the high potential of the present approach for full-spectrum displays, active coatings, and rewritable papers.

CASCADE: Naked eye-detection of SARS-CoV-2 using Cas13a and gold nanoparticles

The COVID-19 pandemic has brought to light the need for fast and sensitive detection methods to prevent the spread of pathogens. The scientific community is making a great effort to design new molecular detection methods suitable for fast point-of-care applications. In this regard, a variety of approaches have been developed or optimized, including isothermal amplification of viral nucleic acids, CRISPR-mediated target recognition, and read-out systems based on nanomaterials.Herein, we present CASCADE (CRISPR/CAS-based Colorimetric nucleic Acid DEtection), a sensing system for fast and specific naked-eye detection of SARS-CoV-2 RNA. In this approach, viral RNA is recognized by the LwaCas13a CRISPR protein, which activates its collateral RNase activity. Upon target recognition, Cas13a cleaves ssRNA oligonucleotides conjugated to gold nanoparticles (AuNPs), thus inducing their colloidal aggregation, which can be easily visualized. After an exhaustive optimization of functionalized AuNPs, CASCADE can detect picomolar concentrations of SARS-CoV-2 RNA. This sensitivity is further increased to low femtomolar (3 fM) and even attomolar (40 aM) ranges when CASCADE is coupled to RPA or NASBA isothermal nucleic acid amplification, respectively. We finally demonstrate that CASCADE succeeds in detecting SARS-CoV-2 in clinical samples from nasopharyngeal swabs.In conclusion, CASCADE is a fast and versatile RNA biosensor that can be coupled to different isothermal nucleic acid amplification methods for naked-eye diagnosis of infectious diseases.

Ultra-fast colorimetric detection of glutathione by magnetic Fe NPs with peroxidase-like activity

The nanozymes-based sensing platforms have been attracted in recent years due to their outstanding performances in the practical applications. In this work, the magnetic Fe nanoparticles (NPs) with peroxidase-like activity was developed for the fast detection of glutathione (GSH). The Fe NPs were facilely prepared through the reduction of iron trichlorrde hexahydrate (FeCl3‧6H2O) by sodium borohydride (NaBH4) at room temperature, exhibiting a merit of simplicity. Significantly, the achieved Fe NPs have high peroxidase-like catalytic activity. At the room temperature, the colorimetric substrates such as 3,3′,5,5′-tetramethylbenzidine (TMB) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) can be rapidly oxidized by Fe NPs with the help of H2O2. After incubated for just 30 s, the catalytic system could achieve a colored solution. Thus, the Fe NPs-based sensing systems can be employed in the development of the colorimetric biosensors with the naked-eye detection.

Dual-aptamer-based enzyme linked plasmonic assay for pathogenic bacteria detection

Development of rapid, sensitive, and selective method for pathogenic bacteria detection is of great importance for food safety, medical diagnostic, and environmental monitoring. Currently, most techniques for low numbers of bacteria detection require advanced instrumentation or skilled operators. Herein, we present a facile colorimetric detection platform for bacterial detection using Ag nanoplates as chromogenic substrate, which takes advantages of the high specificity and affinity of aptamer and the ability of catalase to hydrolyze H2O2 that can etch Ag nanoplates. By introducing catalase to the sandwich structure composed by dual-aptamer recognition strategy, bacteria detection signal is converted to the peak shift of LSPR and colorimetric change. This proposed method allows a fast naked-eye detection of S. aureus at the concentration of 60 CFU/mL based on the combination of streptavidin-biotin system and inherent sensitivity of plasmonic Ag nanoplates. Owing to the high selectivity and sensitivity, as well as the low-cost and good adaptability, this plasmonic assay is expected to be suitable for pathogenic bacteria detection in resource-limited settings.

RPA-Cas12aDS: A visual and fast molecular diagnostics platform based on RPA-CRISPR-Cas12a method for infectious bursal disease virus detection

Infectious bursal disease (IBD), a major disease of birds, is caused by infectious bursal disease virus (IBDV). The disease can lead to immunosuppression, resulting in huge economic losses in the poultry industry. A specific, rapid, and simple detection method is important for the early diagnosis and prevention and control of IBDV. In this study, we established a naked-eye visual IBDV detection method, named “RPA-Cas12aDS”, by combining recombinase polymerase amplification (RPA) with CRISPR-Cas12a-based nucleic acid detection. The detection process can be accomplished in 50 min, and uncapping contamination can be avoided. The detection results can be observed under blue or UV light. We used the RPA-Cas12aDS method to detect IBDV in bursa of Fabricius tissue samples of chickens, and the results were consistent with those obtained using commercial RT-PCR kits. This method presents great potential for visual, rapid, and point-of-care molecular diagnostics of IBDV in poultry.

A low cost yet highly sensitive silver nanoprobe for naked eye detection and determination of bisulphate (HSO4-) in a few real samples

Herein, we report a simple and economical yet highly sensitive and efficient silver nanoresonators based protocol for naked eye detection of a janus-faced ion like bisulphate from its two real samples in real time. The SEM-TEM, DLS, AFM and EDAX alongwith spectroscopic studies have further substantiated our observation in the same context. The quantification of bisulphate in one of its real sample through UV–Vis spectroscopy using these nanoprobes as indicator has also been carried out successfully. The Raman measurements have clearly indicated the rich SERS potential of these silver nanoresonators.

Naked-Eye Detection of Morphine by Au@Ag Nanoparticles-Based Colorimetric Chemosensors.

In this study, we report a novel and facile colorimetric assay based on silver citrate-coated Au@Ag nanoparticles (Au@AgNPs) as a chemosensor for the naked-eye detection of morphine (MOR). The developed optical sensing approach relied on the aggregation of Au@Ag NPs upon exposure to morphine, which led to an evident color variation from light-yellow to brown. Au@Ag NPs have been prepared by two different protocols, using high- and low-power ultrasonic irradiation. The sonochemical method was essential for the sensing properties of the resulting nanoparticles. This facile sensing method has several advantages including excellent stability, selectivity, prompt detection, and cost-effectiveness.

Multi-channel detection of Au(III) ions by a novel rhodamine based probe

Ionic gold species display remarkable features in chemical and biological activities. However, high amount of gold ions, especially Au3+ ions (200 µM), seriously threaten living organisms and vital human organs. Therefore, accurate detection of Au3+ ions is highly desirable. In this work, a novel rhodamine based optical and electrochemical active probe, integrated with triphenylamine and thiophene moiety, exhibited highly selective detection of Au(III) ions compared to the other metal species, such as Ag+, K+, Li+, Na+, Hg2+, Ba2+, Ca2+, Cd2+, Cu2+, Co2+, Mg2+, Mn2+, Ni2+, Pb2+, Zn2+ Pd2+, Al3+, Ce3+, Cr3+, Fe3+ and Cr6+. Exploiting hydrolysis and ring-opening reaction, the probe offers privileged properties such as naked-eye detection (colorimetric), both “turn-on” and “turn-off” fluorescence responses, voltammetric read-out with an anodic shift, low detection limit (340 and 315 nM for “turn-on” and “turn-off”, respectively), rapid response, and applicability in determining Au(III) in complex water samples.

Fast DNA biosensing based on isothermal amplification, unmodified gold nanoparticles, and smartphone detection

The protection of the consumer against foodborne illnesses and fraudulent practices requires methods capable of detecting critical components. Classical instrumental and DNA-based technologies have assay time, portability, and cost limitations. Thus, food control needs alternative methodologies for massive and cost-effective screening. Herein, we report an instrument-free method based on detecting genes that encode proteins related to food allergies and ingredients associated with illegal practices. Tailed recombinase polymerase amplification (tailed-RPA) provided the selective isothermal amplification of target regions. A reproducible and fast optical detection was developed based on the salt-induced aggregation of 15 nm gold nanoparticles (AuNPs). The target presence was directly observed (naked-eye detection) and quantified using a smartphone and RGB image decomposition. The advantages arise from the effective formation of a hybrid complex between non-functionalized nanoparticles and amplification products with a single-strand tail, featuring short incubation time, simplicity, and low sample and reagent volumes. As proof of concept, two targets were determined: trnL gene and ITS region. The first sequence is located in the chloroplast genome of cereals and is valuable to control the adulteration of meat products. The second is a fragment common to the three main gluten-containing cereals, applicable to the indirect detection of this allergen. The novelty also is the integration of a low-cost assay platform and a straightforward interpretation system to foster its implementation in the industry. The RPA-AuNP assay offered a good sensitivity (genomic DNA 0.8 ng), selectivity (absence of unspecific response), reproducibility (standard deviation 2–11%), and accuracy in marketed food products (100%). Therefore, a competitive biosensing system enables better control according to food industry/consumers demands from Farm to Fork strategy.