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[Display omitted] • The development of the LC-based sensing platform for the detection. • It is fulfilled with the assistance of CeO 2 nanomaterials and single-stranded DNA. • Catalase can be analyzed with remarkable sensitivity and excellent specificity. • The detection limit of catalase reaches as low as ∼ 1 mU/mL. • The detection of catalase is successfully achieved in human serum. A briefness, convenient, label-free and sensitive liquid crystal (LC) sensing platform is demonstrated to detect catalase in human serum with the assistance of CeO 2 nanomaterials and the single-stranded DNA (ssDNA). In the presence of H 2 O 2 and ssDNA/CeO 2 nanomaterials complex, a colourful optical appearance of LCs doped with octadecyl-trimethylammonium bromide (OTAB) was observed under a polarized optical microscopy (POM), which is corresponding to the oblique alignment of LCs at the aqueous-LC interface. This can be ascribed to the disruption of the OTAB monolayers by ssDNA that is set free from the surface of CeO 2 nanomaterials in the presence of H 2 O 2. The stronger coordination interaction between H 2 O 2 and CeO 2 nanomaterials causes a replacement for ssDNA. Interestingly, with the hydrolysis of H 2 O 2 by catalase, the LCs exhibit a dim image, which suggests the upright alignment of LCs at the aqueous-LC interface. It is because there is no free ssDNA discharged into the aqueous solution after the hydrolysis of H 2 O 2. Hence, by observing the changes of colourful and dim optical images of LCs, catalase can be analyzed with remarkable sensitivity and excellent specificity. The detection limit of catalase reaches as low as ∼ 1 mU/mL. Besides, the detection of catalase in human serum is also successfully achieved, which makes this assay meets the requirement of practical applications. Therefore, this work offers an effective and appealing strategy for the real-time and label-free detection of catalase in human serum. [ABSTRACT FROM AUTHOR]

This work demonstrates a noninvasive approach to control alignment of liquid crystals persistently and reversibly at fluid interfaces by using a photoresponsive azobenzene-based surfactant dissolved in an ionic liquid (IL), ethylammonium nitrate (EAN). As the first report on the orientational behavior of LCs at the IL/LC interface, our study also expands current understanding of alignment control of LCs at the aqueous/LC interface by adding electrolytes into aqueous solutions. The threshold concentration for switching the optical responses of LCs can be changed just by simply manipulating the ratio of EAN to H2O. This work will inspire fundamental studies and novel applications of using the LC-based imaging technique to investigate various chemical and biological events in ILs. [ABSTRACT FROM AUTHOR]

• A liquid crystal-based Pb2+ sensing platform with high sensitivity and specificity. • It is assisted with DNAzyme and rolling circle amplification on magnetic beads. • The detection limit of Pb2+ reaches as low as 16.7 pM. • It shows excellent performance in detection of Pb2+ in tap water and lake water. Lead ions (Pb2+) are one of the most widespread heavy metal contaminants that pose detrimental impact on environment and human health. We demonstrate a highly sensitive and specific liquid crystal (LC)-based sensing platform for detecting Pb2+ assisted by DNAzyme and rolling circle amplification (RCA). Magnetic beads (MBs) are functionalized with DNA duplexes of the catalytic strands (DNAzymes) and the substrate strands. In the presence of Pb2+, the substrate strands are disassembled due to activation of the DNAzyme, which allows initiation of DNA RCA on MBs. The amplified DNA strands can disrupt arrangement of octadecy trimethyl ammonium bromide monolayers (OTAB), thereby inducing planar orientation of LC molecules at the interface of aqueous and LCs. Thus, LCs exhibit bright appearance. In contrast, RCA cannot be triggered in the absence of Pb2+. Therefore, LC molecules adopt perpendicular orientation at the interface, which induces the dark morphology of LCs. The limit of detection reaches as low as 16.7 pM. It is an improvement of more than two orders of magnitude compared to that of previously reported LC-based sensing approaches. This approach also shows excellent performance in monitoring Pb2+ in tap water and lake water. [ABSTRACT FROM AUTHOR]

The rapid and accurate identification of live pathogens with high proliferative ability is in great demand to mitigate foodborne infection outbreaks. Herein, we have developed an ultrasensitive image-based aptasensing array to directly detect live Salmonella typhimurium (S.T) cells. This method relies on the long-range orientation of surfactant-decorated liquid crystals (LCs) and the superiority of aptamers (apt ST). The self-assembling of hydrophobic surfactant tails leads to a perpendicular/vertical ordered film at the aqueous/LC interface and signal-off response. The addition of apt ST perturbed LCs' ordering into a planar/tilted state at the aqueous phase due to electrostatic interactions between the surfactant with the apt ST , and a signal-on response. Following the conformational switch of apt ST in the presence of live S. typhimurium , a relative reversing signal-off response was observed upon the target concentration. This aptasensor could promptly confirm the presence of S. typhimurium without intricate DNA-extraction or pre-enrichment stats over a linear range of 1–1.1 × 106 CFU/mL and a detection limit of 1.2 CFU/mL within ∼30 min. These results were successfully validated using molecular and culture-based methods in spiked-milk samples, with a 92.61–104.61 % recovery value. Meanwhile, the flexibility of this portable sensing platform allows for its development and adoption for the precise detection of various pathogens in food and the environment. [Display omitted] • An innovative portable LC-aqueous aptasensor is developed for viable bacteria detection. • A signal-off mode was introduced into optical aptasensors based on aptamer-target interaction. • A calibration curve from 100 −106 CFU/mL was utilized for S. typhimurium with a 1.1 CFU/mL LOD. • The aptasensor performs the sensing without any sample pre-enrichment steps. • The LC-aqueous aptasensor achieved sensitive and superbright rapid (∼30 min) detection of live S. typhimurium in food. [ABSTRACT FROM AUTHOR]

This study addressed the limitations of cholesteric liquid crystal (CLC) based microlens arrays, which required submersion of the CLC in water for their formation. We successfully constructed microlens arrays at both the air/CLC/air and water/CLC/air interfaces by doping E7, a nematic host, with a strong chiral dopant, (S)− 1-Phenylethane-1, 2-diyl bis(4-(trans-4-pentyl cyclohexyl) benzoate) (S1011) at different concentrations (0.3, 0.5, and 1 wt%). By spreading the mixture on transmission electron microscopy square-geometry grids, we observed that the lenses thickened at the water/CLC/air interface and thinned at the air/CLC/air interface with increasing dopant concentrations. A non-inverted image on the same side as the object was analyzed, created from the inverted virtual image of the object on the opposite side of the lens. The non-inverted image's focal length ranged from 6–6.24 mm for air/CLC/air and 4.8–3.6 mm for water/CLC/air, corresponding at 0.3, 0.5, and 1 wt% of S1011. Furthermore, the effect of interfacial tension on focal length was also observed by replacing water with sodium dodecyl sulfate (SDS) solution, and it was found that the focal length increased by 60 µm with increasing SDS from 0.1 to 1 mM. These findings suggest that the S1011 doped E7 microlens array can be easily constructed and potentially used in optical technologies. [Display omitted] • This research overcomes the limitations of traditional cholesteric liquid crystal (CLC) lenses. • The construction of microlens arrays at air/CLC/air and water/CLC/air interface is demonstrated. • A detailed analysis of image formation is provided. • The variation of focal length at different interfaces is demonstrated. • This studyhas potential to contribute to advancements in optical devices and systems. [ABSTRACT FROM AUTHOR]

High-throughput screening of lipase inhibitors is critical for developing anti-obesity drugs. Herein, a robust and versatile sensing platform based on the difference in the sliding time of droplets on liquid crystal-infused porous surfaces (LCIPS) is developed to detect lipase inhibitors. Lipase catalyzes glycerol trioleate (GT) to produce oleate that can adsorb at the solution/liquid crystal (LC) interface due to its high amphiphilicity, which impedes the sliding of droplets on LCIPS, resulting in an extended sliding time. However, in the presence of lipase inhibitors, the enzymatic hydrolysis of GT by lipase is inhibited, which shortens the sliding time. The screening of three lipase inhibitors, orlistat, cetilistat, and epigallocatechin gallate (EGCG), popular anti-obesity drugs, is demonstrated to have IC 50 values of 17.45 ± 3.15 nM, 72.15 ± 6.32 nM, and 2.19 ± 0.24 μM, respectively. This study provides a simple, inexpensive, portable, user-friendly, and instrument-free method for rapid, accurate, and high-throughput screening of lipase inhibitors. The LCIPS-based sensing platform is up-and-coming in developing advanced bioanalytical sensors. • A liquid crystal-infused porous surface (LCIPS) sensing platform is developed. • The detection of lipase is fulfilled via the slippery droplet test on the LCIPS. • The production of oleate by the lipase catalysis impedes the droplet sliding. • High-throughput screening of lipase inhibitors is achieved by the LCIPS. [ABSTRACT FROM AUTHOR]

Detecting the ultra-low abundance of heavy metals in real samples remains challenging and it requires the development of high-performance biosensing modalities. This work describes a novel strategy for design an ultra-sensitive liquid crystal (LC) aptasensor, in which the LCs reorientation induced by conformational changes of a triple helix molecular switch (THMS) structure is utilized for the quantitative detection of Pb2+ and Hg2+ ions. The developed aptasensor exhibits a wide linear range with the ultralow detection limits as low as 0.021 aM and 0.068 aM for Pb2+ and Hg2+, respectively. Besides, the results show that other analytes cause no interference. Noteworthy, this sensing strategy is easy to expand for other targets by altering the aptamer sequence without change of the triple-helix structure and can be used for multiple analyte detection. The developed aptasensor is promising powerful platform as a LC AttoSens for precision screening of hazardous residues in food analysis. [Display omitted] • A novel LC AttoSens for precision screening of Pb2+ and Hg2+ ions was developed. • A triple helix molecular switch (THMS) could perturb the liquid crystal alignments. • The developed aptasensor exhibits a wide linear range. • The detection limit of AttoSens is 0.021 aM for Pb2+ ion. • The detection limit of AttoSens is 0.068 aM for Hg2+ ion. [ABSTRACT FROM AUTHOR]

• The surface-anchored liquid crystal droplets are employed for the detection of AFB1. • The interaction of AFB1 and aptamer releases CTAB from the CTAB/aptamer complex. • AFB1 is detected from escape-radial to radial change in the 5CB SADrop configuration. • The limit of detection of AFB1 reaches as low as 10 pg/mL. • The detection of AFB1 is demonstrated in the real samples using peanut oil and rice. 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 (5CB SADrop) are obtained via a solvent evaporation method. The 5CB SADrop 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. [ABSTRACT FROM AUTHOR]

The detection of AFB1 that is a group I carcinogen is significantly important for food safety. Herein, we report a colorimetric liquid crystal (LC)-based assay that allows the ultrasensitive detection of AFB1. When an aqueous solution of a cationic surfactant is transferred onto the LCs dispersed with the aqueous microdroplets containing the anionic surfactants and horseperoxidase (HRP), it triggers the release of HRP due to the interfacial charge interaction. Because HRP can catalyze the colorless 3,3′-5,5′-tetramethylbenzidine (TMB) into yellow products, the response of the LCs dispersed with the aqueous microdroplets to the cationic surfactant is visually determined. In the presence of AFB1, the rolling circle amplification on magnetic beads (MBs) is triggered due to the specific recognition of AFB1 by its aptamer, which results in the generation of long chain single-stranded DNA on MBs. As the cationic surfactants are captured by the negatively charged ssDNA, it prevents the release of HRP into the aqueous solution. In contrast, in the absence of AFB1, HRP is released into the aqueous solution. The developed AFB1 sensing assay shows very good linear relationship with the detection limit of AFB1 determined to be as low as 0.014 pg/mL. In addition, the detection of AFB1 in rice and peanut oil is also examined to demonstrate its capability for the analysis of the real samples. Overall, this method takes advantages of the unique aptamer/target recognition, specific enzymatic reaction, and simple colorimetric assay, which makes it very promising for the ultrasensitive detection of AFB1 in practical applications. [Display omitted] • A colorimetric liquid crystal-based assay for the ultrasensitive detection of AFB1 was developed. • The interfacial charge interactions can induce the release of the encapsulated HRP from the aqueous microdroplets. • The RCA technique has been used to improve the sensitivity and specificity for the detection of AFB1. • The detection limit of AFB1 determined to be as low as 0.014 pg/mL. • The detection of AFB1 in rice and peanut oil is also successfully achieved by this sensor. [ABSTRACT FROM AUTHOR]

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 H 2 O 2 , 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. [Display omitted] • A liquid crystal-based sensing strategy is developed for the detection of uric acid and uricase in body fluids. • The oxidation of uric acid by uricase produces H 2 O 2 and induces release of ssDNA adsorbed on nanoceria. • The released ssDNA causes the orientation transition of the OTAB-doped 5CB sensing platform. • It allows the detection of UA with a linear range of 0.01–10 μM and a limit of detection of 0.001 μM. • Uricase can be detected with a linear range of 20–140 μg/mL and a detection limit of 0.34 μg/mL. [ABSTRACT FROM AUTHOR]

Decorating liquid crystals (LCs) with stimuli-responsive materials provides a bridge between the LCs and the biochemical interactions. The alignments of the LC molecules are particularly sensitive. Even small perturbations to the LC interface can substantially direct the orientation of bulk LC phases, which results in transduction and amplification of the chemical and biological events into readily detectable optical outputs. These characteristics make the LCs extremely alluring for the development of biosensors that allow highly sensitive and label-free detection of biomarkers at the aqueous/LC interface. In this review, we organize the LC-based sensing systems into six groups, including monolayer formation, monolayer removal, monolayer disruption, floating LC droplets, sessile LC droplets, and LC elastomer microspheres. The principle, utilization, advancement, and limitations of each platform for the detection of various biomarkers are discussed in detail, which will help expand our understanding of the development of LC-based sensors for advanced diagnostic and therapeutic approaches. • Liquid crystal-based sensors at the aqueous/LC interface are classified into six groups. • The advancement of each platform is discussed for the detection of biomarkers. • The advantages and limitations of the LC-based sensors are described in detail. • The future improvement of the LC-based sensing platforms is discussed. [ABSTRACT FROM AUTHOR]

• The H 2 O 2 -responsive liquid crystal sensing platform is built via doping 5CB with the surfactant PBEC 14 A. • The detection of catalase is fulfilled by the liquid crystal sensing platform. • The detection limit of catalase reaches as low as 5.5 mU/mL. • It shows excellent performance in detection of catalase in human serum. Abnormal levels of catalase are implicated in multiple clinical diseases, so it is of great importance to monitor the levels of catalase in real samples. In this report, a H 2 O 2 -responsive liquid crystal (LC) sensing platform was developed and applied to the detection of catalase in human serum for the first time. The platform was constructed by doping LCs with a synthesized surfactant, namely N,N-dimethyl-N-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl)tetradecan-1-aminium bromide (PBEC 14 A), which can be decomposed by H 2 O 2. Self-assembled monolayers formed at the aqueous/LC interface when immersing the surfactant-doped LCs into an aqueous solution. Accordingly, the LCs displayed a dark image that indicates a perpendicular state of the LCs at the interface. However, when H 2 O 2 was present in the aqueous solution, the optical image of the LCs became bright that represents a planar state of the LCs at the interface. It is caused by disruption of the surfactant monolayers due to decomposition of PBEC 14 A by H 2 O 2. Interestingly, it was found that the LCs still displayed the dark image when the pre-incubated mixture of catalase and H 2 O 2 was transferred onto the LC sensing platform due to enzymatic hydrolysis of H 2 O 2 by catalase. The detection limit of catalase reached as low as 5.5 mU/mL. In addition, it also shows excellent performance for the detection of catalase in human serum. As a simple and convenient method, it shows high promise in the highly sensitive and label-free detection of catalase in practical applications. [ABSTRACT FROM AUTHOR]

The abnormal levels of trypsin in biological fluids can cause some acute illnesses, such as acute pancreatitis, cystic fibrosis and malnutrition. In this paper, we report the development of an integrated liquid crystal (LC) sensing device for simple, rapid and sensitive detection of trypsin assisted by the surfactant-embedded smart hydrogel. The gelatin hydrogel mixed with CTAB is added into the side channel of the LC sensing device. In the presence of trypsin, the gelatin hydrogel is decomposed, which triggers instant release of CTAB into the aqueous solution. The CTAB molecules are then captured by the LCs and form CTAB monolayers at the aqueous/LC interface, which leads to change of the LC images from the bright to the dark appearance under the crossed polarizers. The integrated LC sensing device has a remarkable detection limit of 3.4 × 10−5 mg/mL. It is successfully employed to single-step detection of trypsin in human serum within 30 min. The integrated LC sensing device with use of the surfactant-embedded hydrogel takes advantages of single-step detection, high portability, remarkable sensitivity and fast response time, which provides a new perspective to facilitate development of user-friendly LC-based sensors. • An integrated liquid crystal sensing device is developed for single-step detection of biomolecules. • The decomposition of the gelatin hydrogel by trypsin triggers release of the surfactant CTAB. • The released CTAB molecules change the LC images from bright to dark. • This user-friendly device has high portability, remarkable sensitivity and fast response time. • It shows excellent performance in detection of trypsin in human serum. [ABSTRACT FROM AUTHOR]

• An α-glucosidase liquid crystal-based assay is developed. • The non-ionic surfactant dodecyl α-D-glucopyranoside is employed to construct the sensing platform. • The sensor can be applied to detect α-glucosidase inhibitors that are anti-diabetic drugs. • The activities of different anti-diabetic drugs are quantitatively determined. The detection of α-glucosidase (AGLU) inhibitors is critical for the screening of anti-diabetic drugs. In this study, we first demonstrate a liquid crystal (LC)-based assay to detect anti-diabetic drugs. When the solution of non-ionic surfactant dodecyl α-D-glucopyranoside (DDG) is introduced onto the LCs, self-assembled monolayers are formed at the aqueous/LC interface, which induces the perpendicular orientation of LC molecules at the interface. Accordingly, the LCs show a dark image. However, when a mixture of AGLU and DDG is introduced onto the LCs, a bright image is observed due to enzymatic hydrolysis of DDG by AGLU, which prevents formation of the surfactant monolayers and results in the planar or tilted orientation of LC molecules at the interface. Using the LC-based AGLU assay, the detection of three AGLU inhibitors that are popular anti-diabetic drugs including acarbose, migliol, and voglibose is demonstrated. In addition, the linear detection ranges and the detection limits of these drugs are also determined. This method provides a simple and powerful strategy to rapidly and accurately detect AGLU inhibitors, which is very promising in the applications of screening anti-diabetic drugs. [ABSTRACT FROM AUTHOR]

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. Image 1 • 5CB doped with the cationic surfactant OTAB is working as the sensing platform. • The arrangement of the OTAB monolayers can be disrupted by ssDNA that undergoes irreversible cleavage by BLM·Fe(II). • The detection limits of BLM and BLMH reach as low as 0.2 nM and 0.3 ng/mL. • The detection is successfully achieved in human serum. [ABSTRACT FROM AUTHOR]

• Building a LC-based sensing platform with enzyme-responsive supramolecular materials. • It has high sensitivity and specificity in detection of organophosphates. • Detection of organophosphates is achieved in lake water and orange juice. Here, we demonstrate use of acetylcholinesterase (AChE)-responsive polyoxometalate (POM)/surfactant supramolecular spheres to build a liquid crystal (LC)-based sensing platform for detection of organophosphorus pesticides. The self-assembled spheres are composed of hybrid materials of a POM, sodium dodecatungstophosphate (PW 12), and a surfactant, myristoylcholine (Myr). It displays dark appearance when the aqueous solution is in contact with LCs supported on the octadecyltrichlorosilane-treated glass deposited with the supramolecular spheres, suggesting perpendicular orientation of LCs at the aqueous/LC interface. In contrast, LCs show bright appearance when the surface-deposited supramolecular spheres are enzymatically hydrolyzed by AChE, corresponding to planar orientation of LCs at the aqueous/LC interface. Detection of organophosphates are successfully achieved as they are potent inhibitors of AChE. The detection limit of the sensing platform reached 0.9 ng/mL for dimethoate. This method can avoid disturbance of external interference with excellent specificity and sensitivity, which makes it very promise in detection of organophosphorus pesticides. [ABSTRACT FROM AUTHOR]