Visual Test Strip Research Articles

Eu(III)-functionalized metal–organic framework as a visual ratiometric fluorescence sensor for rapid discrimination and detection of multiple tetracyclines in agricultural products

The misuse of oxytetracycline (OTC), doxycycline (DOX), tetracycline (TC), and chlortetracycline (CTC) poses a serious threat to human health and it calls for rapid and visual methods. In this study, a novel ratio fluorescent sensor was constructed by simply combining Eu(III) with IRMOF-3. Spectral characterization and DFT theoretical calculations revealed different mechanism of interactions between the MOF-based sensor and different tetracyclines in detail. PCA analysis amplified these differences, enabling the simultaneous identification and differentiation of individual, binary or ternary mixtures of multiple tetracyclines. Subsequently, a rapid fluorescence sensing method (<5 min) for detecting OTC, DOX, TC, and CTC was established with low detection limits of 70, 75, 40, and 168 nM, respectively, which are all below the maximum residue limits by the European Union and the U.S. Food and Drug Administration regulations. A portable visual test strip was also conducted based smartphone with low detection limits of 1 μM, exhibiting an obvious color spectrum transition from blue to purple and finally to pink. Furthermore, the sensor was applied successful to pig feed, milk and veterinary drugs. The results showed good agreement with HPLC-MS/MS analysis.

Green synthesis of chitosan/glutamic acid/agarose/Ag nanocomposite hydrogel as a new platform for colorimetric detection of Cu ions and reduction of 4-nitrophenol

In this study, the green synthesis of chitosan/glutamic acid/agarose/Ag (Chi/GA/Aga/Ag) nanocomposite hydrogel was obtained via in situ reduction of Ag ions during the crosslinking process of chitosan-agarose double network hydrogels. The rich hydroxyl, carboxyl and amino groups in both agarose, chitosan, and glutamic acid can effectively control the growth, dispersion and immobilization of nearly spherical Ag nanoparticles (70 nm) in the Chi/GA/Aga/Ag composite hydrogel. Glutamic acids can act as the structure-directing agents to induce the formation of chitosan/glutamic acid hydrogel. The mechanical strength of the Chi/GA/Aga/Ag composite hydrogel can be enhanced by the introduction of chitosan-agarose double network hydrogels, which guarantees that it can be directly used as a visual test strip of the Cu ions with a lower detection limit of 1 μM and an active catalyst for the reduction of 4-nitrophenol within 18 min. The quantitative and semi-quantitative measurement of Cu ions can be carried out by UV–visible absorption spectroscopy and visual measurement, which provided a convenient, portable, and “naked-eye” solid-state detection methodology.

Photothermal effect-enhanced peroxidase-like performance for sensitive detection of organophosphorus pesticides on a visual test strip

Pesticides pose a serious risk to public health, even in trace amounts. The sensitive, rapid, visual, and on-site detection of pesticides in a real sample remains a challenge. Herein, we report a visual and rapid organophosphorus pesticide (OP) sensing device with excellent sensitivity, ease of application, and specificity based on a photothermal effect-based peroxidase (POD) mimetic. The ultrathin MIL-101-NH2(Fe) (Fe-MOF) shell-coated Au nanobipyramide (NBP) not only possesses POD-like activity, but also exhibits excellent photothermal effect under near-infrared (NIR) light. The results reveal that the excellent photo-to-thermal conversion of the Au NBPs can rapidly heat the MIL-101-NH2(Fe) shell, which subsequently induces a markedly enhanced POD-like activity. Using paraoxon-ethyl as model OP, the combination of the OP inhibition effect on the biocatalytic activity of acetylcholinesterase with the inhibition effect of thiocholine on the colorimetric assays of the POD-mimicking Fe-MOF leads to a significant improved selectivity for OP sensing. In particular, the NIR light irradiation increased the OP detection sensitivity by 100 times. Importantly, based on this detection strategy, a visual test strip with high sensitivity was developed and enabled real-time detection through a simple color analysis software on a smartphone. The successful detection of OP residues in fruit peel using this test strip further confirmed its application potential in real sample analysis.

Smartphone-assisted ratiometric sensing platform for on-site tetracycline determination based on europium functionalized luminescent Zr-MOF

Accurate on-site analysis of tetracycline (TC) is of great research value for ensuring food safety and estimating environmental pollution. Herein, a smartphone-based fluorescent platform for TC detectionhas been developed based on a europium functionalized metal–organic framework (Zr-MOF/Cit-Eu). Based on the inner filter and antenna effect between Zr-MOF/Cit-Eu and TC, the probe exhibited a ratiometric fluorescent response toward TC, resulting in an emission color change from blue to red. Excellent sensing performance was achieved with a detection limit of 3.9 nM, consistent with the linear operation spanning nearly four orders of magnitude. Subsequently, visual test strips based on Zr-MOF/Cit-Eu were prepared, possessing the potential for accurate testing of TC via RGB signals. Finally, the proposed platform was well applied in actual samples with satisfied recoveries (92.27 to 110.22%). This MOF-based on-site fluorescent platform holds great potential on constructing intelligent platform for visual and quantitative detection of organic contaminants.

Label-free and highly selective MOFs-based dopamine detection in urine of Parkinson’s patients

The amount of dopamine (DA) in the body is closely related to the occurrence and development of Parkinson's disease. However, DA detection in real body fluids is still challenging. Here, we developed a high-selectivity and high-sensitivity label-free lanthanide metal organic frameworks (MOFs) to monitor DA in urine samples from Parkinson’s patients. The fluorescent MOF Eu-α-cyclodextrin (CD), prepared by biomineralization under mild conditions, exhibited DA concentration-dependent fluorescence intensity via host–guest complexation. Furthermore, molecular dynamics (MD) simulation analyses quantitatively dissect thermodynamic interactions of cyclodextrin and guest molecules, which systematically reveals the specific recognition mechanism of cyclodextrin and dopamine molecules. A good response for DA in the range of 10-9 to 10-4 M and a limit of detection (LOD) of 0.65 nM were obtained, consistent with the detection range of DA in a variety of biological fluids. Because of the good anti-interference properties of this complex, visual test strips were prepared by the in-situ growth of Eu-αCD nanoparticles on a nitrocellulose (NC) membrane at room temperature, owing to the protein absorbability of NC membranes. The resultant test strips possess the potential for semiquantitative detection of DA by the naked eye. Moreover, we applied Eu-αCD nanoparticles to analyze clinical urine samples from Parkinson's patients, and achieved a low relative error compared with those of commercial HPLC methods. Our work offers an efficient strategy for visual and on-site detection of DA in the clinic, which can assist in early diagnosis of Parkinson's disease.

Novel water-dispersible lanthanide-grafted covalent organic framework nanoplates for luminescent levofloxacin sensing and visual pH detection

Levofloxacin (LVFX) is a fluoroquinolone antibacterial agent and widely used in the treatment of bacterial infections. However, the abuse of LVFX will do great harm to human being, and alkaline urine (pH > 7.0) with decreased solubility of LVFX will further cause adverse side effects. There is an urgent demand and great challenge to construct a mutlifunctional nano-system for the detection of LVFX and pH. We report a novel water-dispersible europium (Eu)-grafted covalent organic framework nanoplates (Eu@CON) with luminescent characteristics of Eu3+. Eu@CON shows high selective and sensitive luminescence sensing for LVFX with a limit of detection (LOD) at 0.51 μM. A visual test strip has been further designed and fabricated for on-site and rapid pH measurement with a detection range from 1 to 4 and 11 to 14. This proof-of-concept study not only reports a new type of luminescent LVFX and pH sensor, but also provides a promising strategy for the design of water-dispersible lanthanide-grafted luminescent CONs to further extends its application in chemo-biosensing.

A chip-based scientific payload technology for visual detection of proteins and its application in spaceflight

Highly sensitive visual detection of proteins in space is often complicated, since bioassay payloads must achieve sensitive detection and environmental adaptability. Microfluidic chips enabling high degrees of integration and automation are a very promising approach for highly sensitive visualized protein detection in space. Here, we present a chip-based, highly integrated payload technology for the visual detection of proteins onboard the Tianzhou-1 cargo spacecraft. This device simply and tightly integrated multifunctional bioassay chips, complex fluid control, and execution of multiple programs to provide highly sensitive protein detection. Based on the delicate design of the microfluidic network, superparamagnetic immunoassay particles were successfully used to achieve immunoaffinity enrichment and visual detection in chips. This method demonstrated good performance compared to traditional visual test strips, showing limits of detection in the picomolar range for interleukin (IL)-6. Results measured in orbit indicated rapid visual detection of IL-6 in cell culture media, confirming the validity of the proposed approach for protein detection in space.

Copper deposition-induced efficient signal amplification for ultrasensitive lateral flow immunoassay

This work describes a novel signal amplification strategy via gold nanoparticle (AuNP)–induced copper deposition to develop a highly sensitive and accurate immunochromatographic platform. Copper deposition–assisted signal amplification (CDASA) was first evaluated on commercially HCG test strip. A lower limit of detection (LOD) over the well-known silver enhancement confirms the great potential of this new approach for the visual test strip. Under an optimal condition, an LOD of 1 pg mL−1 and a wide dynamic range from 1 pg mL−1 to 100 ng mL−1 were achieved by the CDASA with rabbit IgG as a model analyte. In terms of LOD, 2–3 orders of magnitude improvement is received by the CDASA as compared with the conventional test strip without any signal amplification. Potential of the proposed strategy for practical application is also validated by detection of Rabbit IgG in human serum, a mimic clinical sample. The CDASA renders much superiority such as a higher deposition efficiency, lower cost, and better reagent stability over the silver enhancement method. The results can be qualitative and quantitative analysis by the naked eyes and the combination of a flatbed scanner and a free imageJ respectively, eliminating any lab equipment.

Assessment of occupational exposure to gaseous peracetic acid.

In order to assess short-term exposure to peracetic acid (PAA) in disinfection processes, the Authors compared 4 industrial hygiene monitoring methods to evaluate their proficiency in measuring airborne PAA concentrations. An active sampling by basic silica gel impregnated with methyl p-tolyl sulfoxide (MTSO), a passive solid phase micro-extraction technique using methyl p-tolyl sulfide (MTS) as on-fiber derivatization reagent, an electrochemical direct-reading PAA monitor, and a novel visual test strip PAA detector doped with 2,2'-azino-bis (3-ethylbenzothiazoline)-6-sulfonate were evaluated and tested over the range of 0.06-16 mg/m3, using dynamically generated PAA air concentrations. The linear regression analysis of linearity and accuracy showed that the 4 methods were suitable for PAA monitoring. Peracetic acid monitoring in several use applications showed that the PAA concentration (1.8 mg/m3) was immediately dangerous to life or health as proposed by the National Institute of Occupational Safety and Health, and was frequently exceeded in wastewater treatment (up to 7.33 mg/m3), and sometimes during food and beverage processes and hospital high-level disinfection operations (up to 6.8 mg/m3). The methods were suitable for the quick assessment of acute exposure in PAA environmental monitoring and can assist in improving safety and air quality in the workplace where this disinfectant is used. These monitoring methods allowed the evaluation of changes to work out practices to reduce PAA vapor concentrations during the operations when workers are potentially overexposed to this strong antioxidant agent. Int J Occup Med Environ Health 2018;31(4):527-535.

Advances on nanoparticles-tagged visual test strips for the rapid detection of pesticides

The residue of the pesticides affects seriously the quality and safety of traditional Chinese medicine. Pesticide residue has caused ever-growing attention of people at home and abroad. Rapid detection techniques used for rapid screening of pesticide residues have expanded in a fast progress. As one of the fast development methods of rapid detection, visualization test strip based on nanoparticle has received much concern in recent years. This article focused on the classification of detection test strips and key factors on the fabrication of nanoparticle-based visualization test strips used in small molecule pesticides. Moreover, a wide application of nanoparticles-tagged test strips on pesticide residue was reviewed including single residue detection, multi residue detection, as well as quantitative analysis. Finally, the future application of visual test strip for detecting of pesticide residues in traditional Chinese medicine was forecasted, intending to provide the reference for rapid detection techniques on pesticide residues screening in herbal medicine industry.

Far‐Red‐Emitting TEG‐Substituted Squaraine Dye: Synthesis, Optical Properties, and Selective Detection of Cyanide in Aqueous Solution

A comprehensive study of the photophysical properties of triethylene glycol monomethyl ether (TEG)‐substituted squaraine dye SQ1 is presented. SQ1 exhibits strong absorption and intense fluorescence emission in the far‐red spectral region and high photostability. Interestingly, bis‐tegylated SQ1 was characterized to exhibit properties different from its tetrahydroxy analog (SQ2), to which we ascribe attenuation of intermolecular interactions as a result of steric hindrance through introduction of two TEG chains adjacent to the squaraine core. The photophysical properties of SQ1 were also investigated as a function of temperature and pH. In cetyltrimethylammonium bromide (CTAB) micellar media (1.0 mm), the fluorescence quantum yield of SQ1 increased dramatically to 0.22, compared with 0.02 in water. Based on this discovery, SQ1 was found to display excellent sensitivity and selectivity to the presence of cyanide ions (CN–), with a limit of detection of 1.7 µm. The hypothesized CN– sensing mechanism was probed, and visual test strips were developed. This work broadens the family of squaraine dyes and demonstrates SQ1 for use as a fluorescent or visual sensing probe.

Fluorescent and colorimetric detection of Fe(III) and Cu(II) by a difunctional rhodamine-based probe

A new rhodamine B hydrazone derivative (probe L) was synthesized and characterized. The probe L had sufficiently satisfactory selective response to Fe3+ and Cu2+ ions among various interferential metal ions, and high sensitivity with the detection limit of 4.63×10−9M and 5.264×10−7M for Fe3+ and Cu2+ ions, respectively. In the presence of Fe3+, the probe L exhibited turn-on orange fluorescence accompanied by color change from colorless to pink. Toward Cu2+, the probe L showed significant color change from colorless to red purple. These remarkable orange fluorescence and color change made probe L suitable naked-eye identify for Fe3+ and Cu2+ ions. By means of Job's plot, Benesi-Hildebrand studies and FTIR spectra, both 1:1 binding modes (L-Fe3+ and L-Cu2+) were confirmed. The coordination mechanism and turn on/off fluorescence for L-Fe3+ and L-Cu2+ complexes were well explained by theoretical calculations. Moreover, probe L could be used as a quick, simple, visual test strip for Fe3+ and Cu2+ detection.

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Objectives Dipstick urinalysis is widely used for screening of proteinuria in pregnancy. Conflicting results have been reported for diagnostic accuracy between visual and automated methods. We compared semi-quantitative visual and automated dipstick methods with protein:creatinine ratio (PrCr, ⩾30 mg/mmol defined as elevated) in high risk pregnancy. Methods As part of routine clinical care, 517 random midstream urine samples were collected prospectively from consecutive outpatient ( N = 136) and inpatient ( N = 203) pregnant women attending high-risk maternity clinics. Samples were split into two aliquots. The first underwent point-of-care proteinuria testing using visual test strips (Multistix 10SG, Siemens Healthcare Diagnostics, Inc., Tarrytown NY). The second aliquot was sent to the hospital laboratory for analysis by each of two automated dipstick test strips (Multistix 10SG strip, Bayer Clinitek 50; Chemstrip®10 MD, and Urisys 1100®) and PrCr. For PrCr, urinary protein was measured by a pyrogallol red dye-binding method, and creatinine by an enzymatic method. For each of the dipstick methods, positive test thresholds (see Table) were used to determine diagnostic accuracy for PrCr ⩾ 30 mg/mmol. Results Included were 470 (91.7%) urine samples tested by all dipstick methods. The prevalence of proteinuria was low. All dipstick proteinuria methods showed low sensitivity and high specificity for detection of PrCr ⩾ 30 mg/mmol, although visual dipstick urinalysis had lower sensitivity than either automated method. For all dipstick methods, the positive likelihood ratio (LR) was good-excellent, but the negative LR was poor-fair. Conclusions Automated dipstick methods are more sensitive than visual urinalysis for detection of proteinuria, but diagnostic test performance is still poor-fair as a ‘rule-out’ test for proteinuria. Whether the enhanced sensitivity would be worth the cost and training is to be determined. Table 1 . AUC (area under the curve), CI (confidence interval), LR (likelihood ratio). Group 1 Visual Multistix 10SG strip Group 2 Automated Multistix 10 SG, Bayer Clinitek 50 Group 3 Automated Chemstrip® 10 MD, Urisys 1100® Positive test threshold +1 (0.3 g/l) +1 (0.3 g/l) +1 (0.25 g/l) Proteinuria present 36 (7.7%) 83 (17.7%) 59 (12.6%) Sensitivity (%, 95% CI) 50 (38–62) 71 (59–81) 63 (50–74) Specificity (%, 95% CI) 98 (97–99) 91 (87–93) 95 (93–97) Positive LR (95% CI) 40.8 (16.49–100.96) 7.42 (5.30–10.41) 12.83 (8.04–20.49) Negative LR (95% CI) 0.51 (0.40–0.65) 0.32 (0.22–0.47) 0.39 (0.28–0.54) AUC (95% CI) 0.74 (0.66–0.83) 0.81 (0.74–0.88) 0.79 (0.72–0.87) Disclosures M.E. Correa: None. A.C. Halstead: None. A. Cote: None. D.A. De Silva: None. L. Wang: None. P. von Dadelszen: None. L.A. Magee: None.

Quality assessment of visual test strips for home blood glucose monitoring

AbstractA quality control filter‐paper method was applied to the assessment of two glucose enzyme reagent strips — Type A and Type B — in the home environment. Forty insulin‐dependent diabetics, experienced in home blood glucose monitoring, took part in a randomised, cross‐over trial. Marked variation was observed in the accuracy of readings with both strips over a wide range of glucose concentrations. Overall, Type B was found to read consistently higher than the reference filter‐paper method, whereas Type A read consistently higher for reference glucose concentrations &lt; 10 mmol/l, but lower for concentrations ≥10 mmol/l. In particular, both strips were equally poor at detecting filter‐paper concentrations in the hypoglycaemic range. Although both strips have been modified since the study was initiated, the principle of quality control is equally applicable to all other currently used and visually read strips. Recommendations are provided for the quality assessment of all reagent strips employed by patients for home blood glucose monitoring.