In this study, to enhance the capability of metal ions disturbing the orientation of liquid crystals (LCs), we designed a new label-free LC biosensor for the highly selective and sensitive detection of heavy metal ions. This strategy makes use of the target-induced DNA conformational change to enhance the disruption of target molecules for the orientation of LC leading to an amplified optical signal. The Hg(2+) ion, which possesses a unique property to bind specifically to two DNA thymine (T) bases, is used as a model heavy metal ion. In the presence of Hg(2+), the specific oligonucleotide probes form a conformational reorganization of the oligonucleotide probes from hairpin structure to duplex-like complexes. The duplex-like complexes are then bound on the triethoxysilylbutyraldehyde/N,N-dimethyl-N-octadecyl (3-aminopropyl) trimethoxysilyl chloride (TEA/DMOAP)-coated substrate modified with capture probes, which can greatly distort the orientational profile of LC, making the optical image of LC cell birefringent as a result. The optical signal of LC sensor has a visible change at the Hg(2+) concentration of low to 0.1 nM, showing good detection sensitivity. The cost-effective LC sensing method can translate the concentration signal of heavy metal ions in solution into the presence of DNA duplexes and is expected to be a sensitive detection platform for heavy metal ions and other small molecule monitors.

Liquid crystals (LCs) are materials that can exhibit the mobility of liquids and the anisotropy of solid crystals. The long-range orientational order and optical anisotropy of LC molecules can transform chemical and biomolecular binding events into amplified optical signals that can be easily observed, even with naked eye. [1][2][3][4][5] Since Abbott and coworkers [1] initiated the field of study using LCs as sensing elements in the detection of biomolecules, liquid-crystalbased biosensing detection has attracted particular attention, because it can localize biomolecules to specific regions of a substrate with micrometer resolution, and the procedure can be carried out under ambient lighting even without the need for electrical power. Specifically, it is of great potential for providing highly sensitive and low-cost bioassays performed away from central laboratories. [6][7][8][9][10][11][12][13][14][15][16][17][18] Abbott and co-workers [1,2,6,7] reported that parallelrubbed bovine serum albumin film and obliquely deposited nanostructured gold film can aid the alignment of LCs to the direction of rubbing or depositing, the specific biomolecular binding events (such as antibody-antigen, protein-ligand, or protein-protein recognition events) can mask the nanostructured grooves, leading to distinguishable orientations of LCs supported on these surfaces. Yang and co-workers [8] developed protein assays on plain glass substrates coated with an organosilane for inducing the homeotropic alignment of LCs. The method can conveniently provide a yes/no answer when the protein concentration exceeded a critical value. Notwithstanding the versatility and simplicity of these LC biosensing approaches based on biomolecular binding events, the sensitivity is limited by the size and amount of biomolecules. This factor may restrict the LC biosensing technique in the bioassay of low concentrations or trace analytes. Ultrasensitive detection of specific DNA sequences is a field of everincreasing interest [19][20][21][22][23][24] for clinical diagnostics, gene therapy, and a variety of other biomedical applications. Due to the mg mL À1 or nm detection limits, [9][10][11][12] however, the LC biosensing technique based on direct biomolecular binding events is difficult to meet the demand of ultrasensitive DNA assays.There is thus significant interest in seeking signal-enhancement strategies for the LC-based DNA biosensing techniques to circumvent the problem of detection sensitivity.Herein, we exploit a highly sensitive signal-enhanced LC biosensing technique based on enzymatic metal silver deposition. A specific DNA sequence assay was chosen as a proveof-concept model (Scheme 1). First, a chemically functionalized surface on a plane glass slide is obtained by selfassembling a (3-aminopropyl)trimethoxysilane (APS)/N,Ndimethyl-N-octadecyl(3-aminopropyl)trimethoxysilyl chloride (DMOAP) film. DNA immobilization was then achieved by binding a capture DNA probe to the APS/DMOAP film by a cross-linker, followed by hybridizations of a target D...

A novel acetylcholinesterase (AChE) liquid crystal (LC) biosensor based on enzymatic growth of gold nanoparticles (Au NPs) has been developed for amplified detection of acetylcholine (ACh) and AChE inhibitor. In this method, AChE mediates the hydrolysis of acetylthiocholine (ATCl) to form thiocholine, and the latter further reduces AuCl(4)(-) to Au NPs without Au nanoseeds. This process, termed biometallization, leads to a great enhancement in the optical signal of the LC biosensor due to the large size of Au NPs, which can greatly disrupt the orientational arrangement of LCs. On the other hand, the hydrolysis of ATCl is inhibited in the presence of ACh or organophosphate pesticides (OPs, a AChE inhibitor), which will decrease the catalytic growth of Au NPs and, as a result, reduce the orientational response of LCs. On the basis of such an inhibition mechanism, the AChE LC biosensor can be used as an effective way to realize the detection of ACh and AChE inhibitors. The results showed that the AChE LC biosensor was highly sensitive to ACh with a detection limit of 15 μmol/L and OPs with a detection limit of 0.3 nmol/L. This study provides a simple and sensitive AChE LC biosensing approach and offers effective signal enhanced strategies for the development of enzyme LC biosensors.

A renewable amperometric immunosensor has been proposed for the determination of Schistosoma japonium antibody (SjAb) in rabbit serum. A paraffin-graphite-Schistosoma japonium antigen (SjAg) biocomposite, which needs no additional curing, was directly used to construct the immunosensors. The analytical sample containing the desired SjAb was mixed with SjAb labeled with horseradish peroxidase (HRP) to form the incubation solution for the competitive binding assay. Amperometry was used to determine the amount of HRP fixed on the sensor surface, which was related to the content of desired SjAb. Assay conditions were optimized, including the selection of substrate, the loading of SjAg in the biocomposite, the amount of labeled SjAb in the incubation solution, the incubation time, and the temperature. Using o-aminophenol (o-AP) as a substrate, amperometric detection at -200 mV (vs SCE) resulted in a pseudolinear detection range of about 0.36 to 14 microg/mL, with a detection limit of 0.36 microg/mL. Rabbit serum samples with varying infection degrees were analyzed, and the results demonstrated that the concentration that is detectable in this system meets the demands of clinical analyses. A new surface on the immunosensor for use in another competitive assay can be obtained by removing the original one and polishing the surface.

Uranyl ion (UO 2 2+) pollution is a serious environmental problem, and developing novel adsorption materials is essential for UO 2 2+ monitoring and removal. Although some progress is achieved, it is still a challenging task to develop an adsorption material with indicating signal for real-time evaluation of the adsorption degree and the UO 2 2+ concentration. Herein, this paper describes a smart photonic crystal hydrogel (PCH) material, which not only can be used for real-time monitoring function but also can be utilized for UO 2 2+ removal based on the chelation of UO 2 2+ with ligand groups in PCH material. The working principle is based on the binding of a uranyl ion to multiple ligand groups, which results in the shrinkage of PCH material and triggers a blue-shift of diffraction wavelength. Consequently, the adsorption degree and the UO 2 2+ concentration can be sensitively evaluated by measuring the diffraction shift or observing the color change with naked eye. With this PCH material, the lowest detectable concentration for UO 2 2+ is 10 × 10 −9 m, and the maximum adsorption capacity at 298 K is 169.67 mmol kg −1 . In addition, this material also holds good selectivity and regeneration feature, and shows desirable performance for UO 2 2+ analysis in real water samples.

We report a ratiometric surface-enhanced Raman scattering (SERS) nanoprobe for imaging hypoxic living cells or tissues, using azo-alkynes assembled on a single-walled carbon nanotube (SWCNT) surface-functionalized with Ag/Au alloy nanoparticles (SWCNT/Ag/AuNPs). Under a hypoxic condition, azobenzene derivatives preassembled on the surface of the nanostructures are reduced stepwise by various reductases and eventually removed from the surface of the SWCNT/Ag/AuNPs, resulting in the loss of characteristic alkyne Raman bands at 2207 cm–1. Using 2D-band of SWCNTs at 2578 cm–1 as the internal standard, we are able to determine the hypoxia level based on the ratio of two peak intensities (I 2578/I 2207) as demonstrated by the successful detection in different cell lines and rat liver tissue samples derived from hepatic ischemia surgery. By combining the outstanding anti-interference property of alkynes as SERS reporters and the distinct Raman responses of alkynes and SWCNTs in complex systems, this novel ratiometric SERS strategy holds promise in becoming a very useful tool for in vitro and in vivo monitoring of hypoxia in research and clinical settings.

A novel signal enhanced liquid crystal biosensor based on using AuNPs for highly sensitive DNA detection has been developed. This biosensor not only significantly decreases the detection limit, but also offers a simple detection process and shows a good selectivity to distinguish perfectly matched target DNA from two-base mismatched DNA.

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