Paper-based Test Strips Research Articles

Griess reaction-based paper strip for colorimetric/fluorescent/SERS triple sensing of nitrite

This study demonstrates a novel strategy for colorimetric/fluorescent/surface enhanced Raman scattering (SERS) triple-mode sensing of nitrite based on Griess reaction modulated gold nanorods (GNRs)-Azo-gold nanoparticles (GNPs) (GNRs-Azo-GNPs) assembly. The p-aminothiophenol (PATP)-capped GNRs (GNRs@PATP) and 1,8-diaminonaphthalene (DAP)-modified GNPs (GNPs@DAP) are first synthesized through Au–S and Au–N bonds, respectively. Upon being excited at 365nm, the dispersion of GNRs-GNPs (GNRs@PATP and GNPs@DAP) emits cyan fluorescence. Next, the addition of nitrite into the GNRs-GNPs induces the formation of GNRs-Azo-GNPs assembly, resulting in the enhancement of color and decrease of fluorescence. Therefore, the GNRs-Azo-GNPs assembly can not only be used as a naked-eye indicator of nitrite changed from orange-yellow to purple, but also as a highly selective ‘‘fluorescence quenching’’ probe due to the fluorescence resonance energy transfer (FRET) between azo-moiety and DAP. The limit of detection (LOD) for nitrite is 0.05μM by colorimetry and 0.01μM by fluorescence. Meanwhile, the GNRs-Azo-GNPs assembly possesses controllable core–satellites nanostructures and enables on-field SERS detection of nitrite with the LOD of 0.8nM. More importantly, the GNRs-GNPs sensing system can not only be used as a paper-based test strip for on-site fast screening of nitrite with a high sensitivity and selectivity, but also as a SERS substrate for reliable quantitative analysis of nitrite. This study offers a new method for on-site visual detection of nitrite in human urine and meat products, as well as provides a strategy for designing multi-mode sensing platform for various applications.

Self-Diffusion Driven Ultrafast Detection of ppm-Level Nitroaromatic Pollutants in Aqueous Media Using a Hydrophilic Fluorescent Paper Sensor.

Development of fluorescent film probes for toxic nitroaromatic compound pollutants (NACs) such as 2,4,6-trinitrotoluene (TNT) in real water samples implies broad applications in environmental and industrial safety control. Despite many recent advances, there are still some difficult challenges facing this area, for example, the restricted sensitivity and long response time caused by hindered and slow diffusion of aqueous NACs samples inside a dense, solid film. Hence, we report herein a robust fluorescent paper sensor with improved sensing abilities, which is prepared by absorbing hydrophilic pyrene-functionalized polymer uniformly into cellulose-based filter papers. Thanks to the numerous oxygen-containing groups grafted on cellulose papers, they allow passive and ultrafast capillary force driving diffusion of aqueous NACs samples into their hydrophilic matrix. Specifically speaking, these paper sensors can offer efficient self-diffusion paths inside the test strips and immediately bring the pyrene fluorophores and NACs quenchers into close proximity. Therefore, the developed paper-based test strips enable both naked-eye detection of low-ppm-level TNT and ultrafast fluorescence quenching with a response time of only a few seconds, which are difficult to be achieved by conventional film probes.

A Paper-Based Lateral Flow Strip for Protein Biomarker Detection

Protein biomarkers are becoming increasingly important in diagnosis and monitoring of diseases. Paper-based test strip is a promising technique for sensing protein biomarkers in point-of-care (POC) applications. This talk will demonstrate our effort to develop a paper-based test strips for detection of Traumatic Brain Injury (TBI) protein biomarker in blood plasma by utilizing employing surface-enhanced Raman scattering (SERS) for signal transduction. The detection of limit (LOD) of this paper test strip for TBI protein biomarker is lower than the cut off value that is present in patient blood plasma. This paper-based lateral flow device has a potential application in POC setting.

Fluorescence detection of dopamine based on nitrogen-doped graphene quantum dots and visible paper-based test strips

Novel fluorescence detection of dopamine based on nitrogen-doped graphene quantum dots and visible paper-based test strips.

A novel fluorimetric sensing platform for highly sensitive detection of organophosphorus pesticides by using egg white-encapsulated gold nanoclusters

Assays for organophosphorus pesticides (OPs) with high sensitivity as well as on-site screening have been urgently required to protect ecosystem and prevent disease. Herein, a novel fluorimetric sensing platform was constructed for quantitative detection of OPs via tyrosinase (TYR) enzyme-controlled quenching of gold nanoclusters (AuNCs). One-step green synthetic approach was developed for the synthesis of AuNCs by using chicken egg white (CEW) as template and stabilizer. Initially, TYR can catalyze the oxidation of dopamine to dopaminechrome, which can efficiently quench the fluorescence intensity of AuNCs at 630nm based on dynamic quenching process. However, with the presence of OPs, the activity of TYR was inhibited, resulting in the fluorescence recovery of AuNCs. This proposed fluorescence platform was demonstrated to enable rapid detection for OPs (paraoxon as model) and to provide excellent sensitivity with a detection limit of 0.1ngmL−1. Significantly, the fluorescence probe was used to prepare paper-based test strips for visual detection of OPs, which validated the excellent potential for real-time and on-site application.

Paper-Based Test Strips for Detection of Nucleic Acids and Heavy Metals

Paper-based test strips are attracting immense attention because of their simplicity, low cost, portability and short test time. This talk will present our effort to develop the paper-based test strips for detection of nucleic acids and heavy metals. Nanomaterials are utilized to improve the sensitivity. The surface-enhanced Raman scattering and the colorimetric methods are employed for the signal transduction. The effects of the signal transduction method on the sensing performance are studied. The developed paper-based test strips have potential applications in point-of-care testing, especially in the resource-poor settings.

Nanostructured Sensors for Biomedical Diagnosis and Environmental Monitoring

Integration of nanostructured materials into sensors is an effective strategy to improve the performance of sensors, in terms of selectivity, sensitivity, response time and reliability. Herein, we present the design and fabrication of various nanostructured sensors and their applications in biomedical diagnosis and environmental detection. The nanostructured sensors can be integrated with plastic microfluidics and paper-based test strips to enable point-of-care tests. Several types of sensors including surface-enhanced Raman scattering sensors, colorimetric sensors, surface plasmon resonance-enhanced fluorescent sensors and electrochemical sensors are demonstrated for biomolecule and environmental pollutant detection.

Glass fibre paper-based test strips for sensitive SERS sensing

Glass fibre paper-based test strips are established for a fast and cost-effective identification and quantification of analytes by SERS.

Ratiometric Signaling of Hypochlorite by the Oxidative Cleavage of Sulfonhydrazide-Based Rhodamine-Dansyl Dyad.

A reaction-based probe 1 for hypochlorite signaling was designed by the conjugation of two fluorophores, rhodamine and dansyl moieties, by the reaction of rhodamine B base with dansylhydrazine. Probe 1 exhibited pronounced hypochlorite-selective chromogenic and fluorescent signaling behavior over other oxidants used in practical applications, such as hydrogen peroxide, peracetic acid, and ammonium persulfate, as well as commonly encountered metal ions and anions. Signaling was attributed to the hypochlorite-induced oxidative cleavage of the sulfonhydrazide linkage of the probe. In particular, favorable ratiometric fluorescence signaling was possible by utilizing the emissions of the two fluorophores. A detection limit of 1.13 × 10(-6) M (0.058 ppm) was estimated for the determination of hypochlorite. A paper-based test strip was prepared and was used as a semiquantitative indicator for the presence of hypochlorite in aqueous solutions. The probe was also successfully applied for the determination of hypochlorite in practical tap water samples.

Visual and fluorescent detection of tyrosinase activity by using a dual-emission ratiometric fluorescence probe.

In this work, we designed a dual-emission ratiometric fluorescence probe by hybridizing two differently colored quantum dots (QDs), which possess a built-in correction that eliminates the environmental effects and increases sensor accuracy. Red emissive QDs were embedded in the silica nanoparticle as reference while the green emissive QDs were covalently linked to the silica nanoparticle surface to form ratiometric fluorescence probes (RF-QDs). Dopamine (DA) was then conjugated to the surface of RF-QDs via covalent bonding. The ratiometric fluorescence probe functionalized with dopamine (DA) was highly reactive toward tyrosinase (TYR), which can catalyze the oxidization of DA to dopamine quinine and therefore quenched the fluorescence of the green QDs on the surface of ratiometric fluorescence probe. With the addition of different amounts of TYR, the ratiometric fluorescence intensity of the probe continually varied, leading to color changes from yellow-green to red. So the ratiometric fluorescence probe could be utilized for sensitive and selective detection of TYR activity. There was a good linear relationship between the ratiometric fluorescence intensity and TYR concentration in the range of 0.05-5.0 μg mL(-1), with the detection limit of 0.02 μg mL(-1). Significantly, the ratiometric fluorescence probe has been used to fabricate paper-based test strips for visual detection of TYR activity, which validates the potential on-site application.

Selective fluorescence turn-on and ratiometric detection of organophosphate using dual-emitting Mn-doped ZnS nanocrystal probe.

Semiconductor nanocrystals (NCs) possess unique photoluminescent properties which can be used to design fluorescence probes for chemo/biosensing applications. Several have recently emerged that offer excellent turn-on or ratiometric fluorescence chemosensory protocols by sophisticated procedures, but it has been challenging to realize all of these advantages in a single construct. Herein, we develop an intrinsic dual-emitting Mn-doped ZnS nanocrystal-based probe that achieves this goal with turn-on and ratiometric fluorescence response for the determination of organophosphate (diethylphosphorothioate, DEP). The probe relies on the modification of dopamine dithiocarbamate on the surface of NCs and the modulation of dual emission through a photoinduced electron transfer process, which makes use of red fluorescence of Mn(2+) ions doped in the NCs as specific recognition for the target analyte and blue defect emission of the NCs as stable internal reference. In presence of DEP, the red emission of the probe is thus enhanced by switching off the electron transfer pathway, while the blue emission is almost unchanged. With the addition of different amounts DEP, the two emission intensity ratios gradually vary and display color changes from dark-blue to purple to red. Thus, this method generates turn-on and ratiometric fluorescence signals for quantitative and visual detection of the analyte. Significantly, the dual-emitting probe has been used to fabricate paper-based test strips for visual detection of DEP residues, which validate the method for its rapid, on-site, and visual identification.

Detection of bacteria using inkjet-printed enzymatic test strips.

Low-cost diagnostics for drinking water contamination have the potential to save millions of lives. We report a method that uses inkjet printing to copattern an enzyme–nanoparticle sensor and substrate on a paper-based test strip for rapid detection of bacteria. A colorimetric response is generated on the paper substrate that allows visual detection of contamination without the need for expensive instrumentation. These strips demonstrate a viable nanomanufacturing strategy for low-cost bacterial detection.

A naphthalimide-based azo colorimetric and ratiometric probe: synthesis and its application in rapid detection of cyanide anions

A naphthalimide-based azo dye (1) used as a colorimetric and ratiometric probe for the detection of CN− was synthesized by incorporating a salicylaldehyde moiety, which acts as a recognition unit, to the naphthalimido diazonium salt. Upon reacting with CN−, probe 1 displays dramatic colour changes rapidly from yellowish to red, corresponding to the absorption band shift from 408 nm to 497 nm. The colorimetric probe allows ratiometric detection of CN− with a linear range of 2–45 μM and a LOD (limit of detection) of 0.4 μM. In the optimized H2O/DMSO (7/3, v/v) mixed solvent, probe 1 displays excellent selectivity for CN− over other anions. In addition, 1 was successfully employed to prepare the filter paper-based test strips which can be used to monitor CN− conveniently, and the discernible concentration of CN− can be as low as 20 μM.

Lab-on-a-Chip Magneto-Immunoassays: How to Ensure Contact between Superparamagnetic Beads and the Sensor Surface.

Lab-on-a-chip immuno assays utilizing superparamagnetic beads as labels suffer from the fact that the majority of beads pass the sensing area without contacting the sensor surface. Different solutions, employing magnetic forces, ultrasonic standing waves, or hydrodynamic effects have been found over the past decades. The first category uses magnetic forces, created by on-chip conducting lines to attract beads towards the sensor surface. Modifications of the magnetic landscape allow for additional transport and separation of different bead species. The hydrodynamic approach uses changes in the channel geometry to enhance the capture volume. In acoustofluidics, ultrasonic standing waves force µm-sized particles onto a surface through radiation forces. As these approaches have their disadvantages, a new sensor concept that circumvents these problems is suggested. This concept is based on the granular giant magnetoresistance (GMR) effect that can be found in gels containing magnetic nanoparticles. The proposed design could be realized in the shape of paper-based test strips printed with gel-based GMR sensors.

Tailoring Sol–Gel-Derived Silica Materials for Optical Biosensing

The last two decades have seen a revolution in the area of sol–gel-derived materials as media for the immobilization of biomolecules for biosensor fabrication. Such materials are suitable for the entrapment of a range of biomolecules, from enzymes to antibodies and even functional nucleic acids (FNA) such as aptamers and DNA enzymes. Recent progress in the development of “protein friendly” sol–gel processing methods has allowed these materials to be utilized as components of numerous biosensors, using delicate biomolecules such as luciferease and kinases, or even membrane-bound receptors as biorecognition elements. In addition, such materials have proven to be particularly versatile in the fabrication of biosensors, being amenable to methods such as dipcasting, contact printing, or even noncontact inkjet printing to form a bioselective coating on a range of substrates. In this review, we provide an overview of advances in biofriendly sol–gel processing methods developed in our research group and others, and we highlight accomplishments in the immobilization of both proteins and FNA within silica based materials. We then describe methods for interfacing biomolecule-doped materials to optical biosensors, with emphasis on fiber optic sensors, microarray-based multianalyte sensors and bioactive paper-based test strips. In each case, the material processing requirements for fabrication of different devices is emphasized. Finally, a brief perspective on potential future areas of research in the field of sol–gel based biocomposites is provided.

Laboratory-scale protein striping system for patterning biomolecules onto paper-based immunochromatographic test strips.

A method for patterning narrow lines of biomolecules onto nitrocellulose membranes using laboratory syringe pumps is described. One syringe pump is used to drive the biomolecule solution through a needle, while another modified syringe pump acts as a one-dimensional translation stage, moving the needle across the membrane much like a pen. This method consumes very small volumes of reagents, and is a viable option for laboratory-scale fabrication and prototyping of point-of-care rapid diagnostic test strips.

Determination of Cr(VI) concentration in diluted samples based on the paper test strip method

At present, there are many methods for Cr(VI) concentration determination in diluted samples, however, these methods have their own inherent drawbacks, such as long response time, complicated pretreatment, expensive equipment etc. In this paper, a paper-based test strip method specific for determination of diluted Cr(VI) samples was developed. In this method, Aliquat 336, as an anion exchanger was loaded into filter paper to form a test strip. This test strip was used to pre-concentrate Cr(VI) when contacting with the diluted Cr(VI)-containing solution. The Cr(VI)-containing test strip was then immersed into a diphenylcarbazide (DPC) solution (a color forming solution), and the color intensity was correlated to the Cr(VI) concentration. The detection range of the present method was found to be 0.02-1.50 mg/L. The results also showed that the method gave a high selectivity for Cr(VI) in the diluted samples to be tested. The method was applied to synthesized samples and the results, which were compared to those from a reference method, showed that the developed method is an effective, reliable way for Cr(VI) determination in diluted samples.

Development of cellulosic paper-based test strips for Cr(VI) determination

Paper-based test strips specific for the Cr(VI) determination in aqueous solutions were developed by impregnating a color-forming reagent, diphenylcarbazide, and a quaternary ammonium salt (Aliquat 336) into paper sheets. The results showed that the quaternary ammonium salt could effectively retain the colored complex in the paper substrate. This paper-based test strip showed a high selectivity for Cr(VI) in the samples to be tested. The method was applied to synthetic samples, and the results were compared to these from a reference method. The current work demonstrated that with a color chart, this portable paper-based test strip has the potential to be used for field screening or on-site semi-quantitative analysis.