A biosensor method based on surfactant-mediated surface droplet evaporation for the detection of Aflatoxin B1.

Aflatoxin B1 (AFB1) is a common mycotoxin that is of significant global concern due to its impact on food safety. Herein, we innovatively develop a sensing platform to detect AFB1 based on evaporation of surfactant solutions on the hydrophobic surface, resulting in dried patterns with varied sizes. The surfactant CTAB solution produces a relatively large dried pattern due to the surface wetting. However, the reduction in the dried pattern size is found when the mixture of CTAB and AFB1 aptamer is tested, because the formation of CTAB/aptamer complex. Moreover, the dried pattern size of the mixture of CTAB, aptamer, and AFB1 increases due to the specific binding of AFB1 to its aptamer. Using this innovative strategy, the AFB1 detection can be fulfilled with a detection limit of 0.77 pg/mL. As a simple, convenient, inexpensive, and label-free method, the surfactant-mediated surface droplet evaporation-based biosensor is very promising for various potential applications.

Surface-anchored liquid crystal droplets for the semi-quantitative detection of Aflatoxin B1 in food samples.

Aflatoxin B1 (AFB1) is a common food mycotoxin that can cause various diseases. Therefore, reliable detection methods are required to ensure food safety against mycotoxins. In this study, we design a liquid-crystal (LC)-based assay for rapid detection of AFB1 in food samples. The surface-anchored LC droplets on glass (5CBSADrop) are obtained via a solvent evaporation method. The 5CBSADrop displays a four-leaf clover appearance that corresponds to an escape-radial configuration in a mixture of CTAB and AFB1 aptamer. Interestingly, they adopt a radial configuration in the mixture of CTAB, AFB1, and its aptamer. Using this approach, AFB1 can be detected using only 1 µL of the aqueous solution with a minimum detection concentration of 10 pg/mL. This LC-based sensing platform provides simple operation, remarkable sensitivity, high selectivity, low cost, and excellent portability without the use of any bulky instrument, which is very promising in rapid on-field detection of mycotoxins.

Liquid crystal-based sensitive and selective detection of uric acid and uricase in body fluids.

The abnormal levels of uric acid (UA) in body fluids are associated with gout, type (II) diabetes, leukemia, Lesch-Nyhan syndrome, uremia, kidney damage, and cardiovascular diseases. Also, the presence of uricase (UOx) symbolizes genetic disorders and corresponding complications. Therefore, the detection of UA and UOx in the body fluids is significant for clinical diagnosis. 4-Cyano-4'-pentylbiphenyl (5CB, a nematic liquid crystal (LC)) was doped with octadecyl trimethylammonium bromide (OTAB, a cationic surfactant), which formed a self-assembled monolayer at the aqueous/5CB interface. The UOx-catalyzed oxidation of UA yielded H2O2, releasing the single-strand deoxyribonucleic acid (ssDNA) from the nanoceria/ssDNA complex. The interaction of the released ssDNA with OTAB disrupted the monolayer at the aqueous/5CB interface, which resulted in a dark to bright change when observed through a polarized optical microscope. The LC-based sensor allowed the detection of UA with a linear range of 0.01-10 µM and a limit of detection (LOD) of 0.001 µM. The UA detection was also performed in human urine samples and the results were comparable to that of a standard commercial colorimetric method. Similarly, the detection of UOx was performed, with a noted linear range of 20-140 µg/mL. The LOD was as low as 0.34 µg/mL. The detection of UOx was also demonstrated in human serum samples with excellent performance. This method provides a robust sensing platform for the detection of UA and UOx and has potential for applications in clinical analysis.

A portable digital optical kanamycin sensor developed by surface-anchored liquid crystal droplets.

There is an increase in demand to develop simple, convenient, and low-cost approaches for rapid and label-free detection of antibiotics. Herein, we propose a new principle for the detection of kanamycin using the surface-anchored liquid crystal (LC) droplets. The optical images of the LC droplets uniformly change from four-clover, uniformly dark, and dark cross appearance gradually with the increase of surfactant concentration. The detection of kanamycin is fulfilled with the aid of a cationic surfactant cetyltrimethylammonium bromide (CTAB) and a kanamycin aptamer. The LC droplets show uniformly dark appearance and four-clover appearance in the presence of the aqueous solutions of CTAB and CTAB/aptamer complex, respectively. However, the specific binding of kanamycin to its aptamer can release the CTAB, which induces the uniformly dark appearance of the LC droplets. A portable device is built to measure the optical luminance of the LC droplets. This system can detect kanamycin with a concentration below 0.1 ng/mL (~0.17 nM) and also allows the detection of kanamycin in real samples such as milk and honey. Therefore, it is very promising in the development of new types of LC-based sensors by the surface-anchored LC droplets assisted with a portable optical device.

Detection of bleomycin and its hydrolase by the cationic surfactant-doped liquid crystal-based sensing platform.

Bleomycin (BLM) is a broadly used antibiotic to treat different types of cancer. It can be hydrolyzed by bleomycin hydrolase (BLMH), which eventually influences the anti-tumor efficacy of BLM. Therefore, it is particularly important to detect BLM and BLMH. Herein, we demonstrated highly sensitive detection of BLM and BLMH by a simple and convenient liquid crystal (LC)-based sensing platform for the first time. 5CB (a nematic LC) doped with the cationic surfactant OTAB was working as the sensing platform. When the OTAB-laden 5CB interface was in contact with an aqueous solution of ssDNA, LCs displayed a bright image due to disruption of the arrangement of OTAB monolayers by ssDNA, indicating the planar orientation of LCs at the aqueous/LC interface. When BLM·Fe(II) and ssDNA were both present in the aqueous solution, ssDNA underwent irreversible cleavage, which prevented disruption of the arrangement of OTAB monolayers. Accordingly, LCs showed a dark image, suggesting the homeotropic orientation of LCs at the aqueous/LC interface. However, when BLM·Fe(II) was enzymatically hydrolyzed by BLMH, LCs remained the bright image. This approach showed high sensitivity for the detection of BLM and BLMH with the limits of detection of 0.2 nM and 0.3 ng/mL, respectively. Besides, the detection of BLM and BLMH was successfully achieved in human serum. This method has the advantages of high sensitivity, robust stability, simple operation, low cost, and easy detection through naked eyes, which makes it a potential candidate for applications in clinical analysis.

A spherical metal-organic coordination polymer for the microextraction of neonicotinoid insecticides prior to their determination by HPLC.

The authors describe a new spherical metal-organic coordination polymer (MOCP) for use as an adsorbent in solid-phase microextraction (SPME). By applying the ions Co(II), Fe(II), Cu(II), and Zn(II) in these polymers, MOCP with different morphology were obtained. The respective coatings for SPME display different extraction efficiency towards neonicotinoid insecticides (neo-nics). The Co(II)@MOCP coating displays an improved extraction capability for neo-nics when compared to the four commercially available coatings studied. Following extraction with the Co(II)@MOCP-coated fiber, the neo-nics were eluted using 1 mL of trifluoroacetic acid/acetonitrile solution and quantified by high performance liquid chromatography. The method, when applied to spiked honey samples, has good linearity (0.5-600 µg kg-1) and a low limit of detection (0.05-0.15 µg kg-1). The precision (n = 6) for a single fiber was in the range of 3.6-8.3%. The reproducibility (for n = 5) from fiber-to-fiber ranges between 5.4 and 8.8%. The Co(II)@MOCP-coated fiber can be reused more than 80 times without any apparent reduction in its performance. In addition, the relative recoveries from spiked honey samples are very good (91.5%-103.5%). Graphical abstract A spherical metal-organic coordination polymer (MOCP) was synthesized under the regulation of Co(II) and used for the solid-phase microextraction (SPME) of neonicotinoid insecticides found in honey.

Ultra-high-pressure-assisted extraction of wedelolactone and isodemethylwedelolactone from Ecliptae Herba and purification by high-speed counter-current chromatography.

Ultra-high-pressure extraction combined with high-speed counter-current chromatography was employed to extract and purify wedelolactone and isodemethylwedelolactone from Ecliptae Herba. The operating conditions of ultra-high-pressure extraction were optimized using an orthogonal experimental design. The optimal conditions were 80% aqueous methanol solvent, 200 MPa pressure, 3 min extraction time and 1:20 (g/mL) solid-liquid ratio for extraction of wedelolactone and isodemethylwedelolactone. After extraction by ultra-high pressure, the extraction solution was concentrated and subsequently extracted with ethyl acetate; a total of 2.1 g of crude sample was obtained from 100 g of Ecliptae Herba. A two-phase solvent system composed of petroleum ether-ethyl acetate-methanol-water (3:7:5:5, v/v) was used for high-speed counter-current chromatography separation, by which 23.5 mg wedelolactone, 6.8 mg isodemethylwedelolactone and 5.5 mg luteolin with purities >95% were purified from 300 mg crude sample in a one-step separation. This research demonstrated that ultra-high-pressure extraction combined with high-speed counter-current chromatography was an efficient technique for the extraction and purification of coumestans from plant material.

Rapid purification of antioxidants from Magnolia officinalis by semi-prep-HPLC with a two-step separation strategy guided by on-line HPLC-radical scavenging detection.

A rapid and accurate strategy of screening, identification, and purification of antioxidants from natural medicines was put forward in this work, and it was applied to discover the antioxidants from magnolia officinals Rahd. et Wils. On-line HPLC-DPPH combined with electrospray ionization time-of-flight mass spectrometry was employed for the rapid screening and potential identification of the antioxidants. Semi-prep-HPLC with two-step separation procedure was employed for the separation and purification of the representative compounds (the first step: compounds 1-4 were obtained by gradient elution; the second step: compounds 5-7 were obtained by isocratic elution). NMR spectroscopy, mass spectrometry, and UV spectroscopy were used for further structural identification, and the activity of the compounds was verified by in vitro assay. With this method, 28 compounds with antioxidant activity were discovered in the extraction. After the preparation and purification, seven compounds with the purity over 95% were get, which were identified as syringing, magnoloside B, magnoloside A, magnoloside F, magnolol, obvatol and honokiol. The results of in vitro assay showed that these seven compounds all had higher DPPH scavenging activity. Thus, all the results suggested that this work provide a more rapid, accurate and efficient methodology to achieve the screening, characterization and preparation of antioxidative constituents from complex natural products under active guidance.