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Antimony is highly toxic and a key water pollutant, which needs to be monitored closely. To date, however, most analytical methods for antimony detection are quite limited because they are complicated, expensive, and not suitable for real-time monitoring of antimony. In this study, a label-free and rapid method for antimony ions (Sb 3+ ) detection is developed based on liquid crystals and a 10-mer poly-adenine oligonucleotide as a specific recognition probe for the first time. The working principle is based on the binding of the oligonucleotide to Sb 3+ , which weakens the interaction between the oligonucleotide and cationic surfactants. As a result, the event induces a planar-to-homeotropic orientational change of liquid crystals and a bright-to-dark optical change under crossed polars. This liquid crystal-based optical sensor exhibits a rapid response to Sb 3+ in 10 s, a detection range between 20 nM and 5 μM, and a detection limit at 6.7 nM calculated from 10-mins assay time. It also shows good selectivity against other metal ions including Ag + , Cd 2+ , Cu 2+ , Fe 3+ , K + , Mg 2+ , Mn 2+ , Na + , Pb 2+ , and Zn 2+ . Moreover, this system can be used to detect Sb 3+ in aqueous solutions with different pH or ionic strengths. This simple, fast, and low-cost liquid crystal-based sensing approach with high sensitivity and selectivity has a high potential for detecting Sb 3+ in natural environments and industrial wastewater., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interestsDan Luo has patent #202310002611.9 issued to Southern University of Science and Technology., (Copyright © 2023 Elsevier B.V. All rights reserved.)

As an emerging stimuli-responsive material, liquid crystal (LC) has attracted great attentions beyond display applications, especially in the area of biochemical sensors. Its high sensitivity and fast response to various biological or chemical analytes make it possible to fabricate a simple, real-time, label-free, and cost-effective LC-based detection platform. Advancements have been achieved in the development of LC-based sensors, both in fundamental research and practical applications. This paper briefly reviews the state-of-the-art research on LC sensors in the biochemical field, from basic properties of LC material to the detection mechanisms of LC sensors that are categorized into LC-solid, LC-aqueous, and LC droplet platforms. In addition, various analytes detected by LCs are presented as a proof of the application value, including metal ions, nucleic acids, proteins, glucose, and some toxic chemical substances. Furthermore, a machine-learning-assisted LC sensing platform is realized to provide a foundation for device intelligence and automatization. It is believed that a portable, convenient, and user-friendly LC-based biochemical sensing device will be achieved in the future.

We report a label-free and simple approach for the detection of glycoprotein-120 (gp-120) using an aptamer-based liquid crystals (LCs) biosensing platform. The LCs are supported on the surface of a modified glass slide with a suitable amount of B40t77 aptamer, allowing the LCs to be homeotropically aligned. A pronounced topological change was observed on the surface due to a specific interaction between B40t77 and gp-120, which led to the disruption of the homeotropic alignment of LCs. This results in a dark-to-bright transition observed under a polarized optical microscope. With the developed biosensing platform, it was possible to not only identify gp-120, but obtained results were analyzed quantitatively through image analysis. The detection limit of the proposed biosensing platform was investigated to be 0.2 µg/mL of gp-120. Regarding selectivity of the developed platform, no response could be detected when gp-120 was replaced by other proteins, such as bovine serum albumin (BSA), hepatitis A virus capsid protein 1 (Hep A VP1) and immunoglobulin G protein (IgG). Due to attributes such as label-free, high specificity and no need for instrumental read-out, the presented biosensing platform provides the potential to develop a working device for the quick detection of HIV-1 gp-120.

We report a surface plasmon resonance (SPR) biosensor for online detection of glyphosate. The surface of the sensing element is decorated with an oligopeptide, TPFDLRPSSDTR, which is identified by using phage display library. This oligopeptide shows high binding specificity for glyphosate (KD = 8.6 μM), probably because of the presence of R and D in the oligopeptide. To detect glyphosate in buffer solution, an SPR gold sensor chip is modified by using the oligopeptide with a surface density of 0.6 1/nm(2). The sensitivity of this oligopeptide-functionalized SPR biosensor is 1.02 RU/μM whereas the limit of detection (LOD) is 0.58 μM. This oligopeptide functionalized SPR biosensor also shows good specificity against other analytes such as glycine, thiacloprid, and imidacloprid.

We report a functional protease assay in which liquid crystals (LCs) are used as signal reporters to transduce the test results into optical signals. In this assay, an oligopeptide substrate (CLSELDDRADALQAGASQFESSAAKLKRKYWWKNLK) is used as a probe. This oligopeptide can be cleaved by α-chymotrypsin at multiple locations and become smaller fragments after the cleavage. When the original oligopeptide is immobilized on a solid surface, its long flexible oligopeptide chain is able to influence the orientation of a thin layer of LC supported on the surface, as is evident as a bright spot on the surface. In contrast, when the shorter oligopeptide fragments are immobilized on the same surface, their shorter, less flexible chains cannot disrupt the orientation of LC, and a dark spot is observed. On the basis of the dark or bright signal from LC, α-chymotrypsin in buffer solution or complex media such as chicken broth can be detected by using the naked eye. However, when the incubation time is 3h, the limit of detection (LOD) for α-chymotrypsin in buffer solution is 50 ng/mL, whereas that in chicken broth is only 500 ng/mL. Unlike traditional antibody-based assays which show little difference between active and inactive α-chymotrypsin, only active protease can be detected in this assay. This study shows the potential utility of LCs for detecting functional proteases with good specificity and sensitivity., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Immunobiosensors are emerging as powerful tools for diagnostic applications. In this paper, we exploit optical properties of liquid crystal (LC) and the specific epitope-antibody interaction to develop an optical immunobiosensor which can be used to detect monoclonal anti-FLAG M2, a model antibody. The sensitive layer of this immunobiosensor is a monolayer of immobilized oligopeptide CDYKDDDDK (FLAG) at an LC/aqueous interface. The linear oligopeptide can function as an epitope which can be recognized by anti-FLAG M2. When the LC is modified with 50 μM of FLAG and then exposed to an aqueous solution containing anti-FLAG, anti-FLAG binds to the immobilized FLAG epitope and triggers orientational transition of LC. Because of the optical birefringence of the LC, the orientational transition is accompanied by changes in the optical images of LC from dark to bright under crossed polarizers. The detection limit for the system is 27 ng/mL of anti-FLAG, and the response time is < 1 h. The binding of anti-FLAG to its motif FLAG oligopeptide is also very specific. When a variant epitope CDAKDDDDK is used, no apparent optical response can be observed after the addition of anti-FLAG., (Copyright 2010 Elsevier B.V. All rights reserved.)

Semiconducting nanowires have the potential to function as highly sensitive and selective sensors for label-free detection of biological and chemical species. In this paper, we describe the preparation and applications of oligopeptide-modified single crystal silicon nanowire (SiNW) arrays as multichannel metal ion sensors. Because these SiNW arrays were fabricated by using a "top-down" process, a very high density of individually addressable SiNW (180 SiNWs grouped into 36 clusters) can be manufactured on a single chip. Furthermore, after two different SiNW clusters are modified with Pb(2+)-selective and Cu(2+)-selective oligopeptide, respectively, concentrations of Pb(2+) and Cu(2+) in aqueous solutions can be detected simultaneously and selectively in two different channels. By using the SiNW arrays, we successfully achieved a detection limit of 1 nM for Pb(2+) and 10 nM for Cu(2+), respectively. These results demonstrate the potential utility of oligopeptide-modified SiNW arrays for highly sensitive and selective chemical and biological sensing applications.

We report a liquid crystal (LC)-based sensor for real-time and label-free identification of phospholipase-like toxins. Beta-bungarotoxin exhibits Ca(2+)-dependent phospholipase A(2) activity whereas alpha-bungarotoxin and myotoxin II do not exhibit any phospholipase activity. The sensor can selectively identify beta-bungarotoxin, when it hydrolyzes a phospholipid monolayer self-assembled at aqueous-LC interface, through orientational responses of LCs. As a result, optical signals that reflect the spatial and temporal distribution of phospholipids during the hydrolysis can therefore be generated in a real-time manner. The sensor is very sensitive and requires less than 5pg of beta-bungarotoxin for the detection. When phospholipase A(2) inhibitors are introduced together with beta-bungarotoxin, no orientational response of LCs can be observed. In addition, the regeneration of the sensor can be done without affecting the sensing performance. This work demonstrates a simple and cost-effective LC-based sensor for identifying phospholipase-like toxins and for screening compound libraries to find potential toxin inhibitors.

In this paper we present a study of using oxygen plasma for chemically modifying inert hydrocarbon self-assembled monolayers of octadecyltrichlorosilane (OTS-SAMs) and rendering active surfaces for protein immobilization. Detailed surface modification and protein immobilization were characterized by using ellipsometry, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared-attenuated total reflectance spectroscopy, and fluorescence microscopy. Our XPS results showed that the surface reaction between OTS-SAMs and oxygen plasma can generate new surface functional groups such as alcohol (C-O), aldehyde (C=O), and carboxylic acid (O-C=O), and their compositions can be controlled by using different treatment times and powers. A short treatment time ( approximately 1 s) and high power (10 W) can lead to a higher density of aldehyde groups, which can serve as linker groups for protein immobilization through the formation of Schiff bases with the amine groups of proteins. By using the fluorescence immunostaining method, we confirmed that human immunoglobulin (IgG) can be immobilized on a glass slide, only if the surface was decorated with OTS-SAMs and if the OTS-SAMs were pretreated with oxygen plasma. The protein immobilized on the oxygen-plasma-treated surface can only be recognized by using a highly specific antibody, FITC-anti-IgG, but not FITC-anti-biotin.