Label-free detection of Aβ-42: a liquid crystal droplet approach for Alzheimer's disease diagnosis

This study introduces a biosensor based on liquid crystals (LC) designed to detect the Aβ-42 biomarker, commonly associated with Alzheimer's disease. The sensor utilizes LC droplets created using a PEI/Tween-20 surfactant mixture, arranged radially in an aqueous solution. These droplets are coated with the Aβ1-16 antibody, enabling the detection of the Aβ1-42 biomarker. The key advantage of this biosensor lies in its ability to directly translate the antigen-antibody interaction into a change in the molecular orientation of the LC droplets, simplifying the detection process by removing additional procedural steps. Specifically, this immunoassay induces a transformation in the nematic droplets orientation from radial to bipolar upon successful antigen binding. When only the Aβ1-16 antibody coated the LC droplets, no change in orientation was detected, confirming the reaction's specificity. The orientation shift in the LC droplets indicates the formation of an immunocomplex between the Aβ1-16 antibody and the Aβ1-42 antigen. The LC droplet immunoassay effectively detected Aβ1-42 antigen concentrations ranging from 45 to 112.5 μM, with the Aβ1-16 antibody immobilized on the droplets at a concentration of 1 μg mL-1. These findings suggest that the LC microdroplets' orientational behavior can be harnessed to develop a biosensor for the in vivo detection of various proteins or pathogens in a PBS aqueous medium. Owing to its label-free nature and distinct optical signaling, this LC droplet-based immunoassay holds promise for further development into a cost-effective, portable diagnostic tool.

Liquid Crystal Droplet-Based Biosensors: Promising for Point-of-Care Testing

The development of biosensing platforms has been impressively accelerated by advancements in liquid crystal (LC) technology. High response rate, easy operation, and good stability of the LC droplet-based biosensors are all benefits of the long-range order of LC molecules. Bioprobes emerged when LC droplets were combined with biotechnology, and these bioprobes are used extensively for disease diagnosis, food safety, and environmental monitoring. The LC droplet biosensors have high sensitivity and excellent selectivity, making them an attractive tool for the label-free, economical, and real-time detection of different targets. Portable devices work well as the accessory kits for LC droplet-based biosensors to make them easier to use by anyone for on-site monitoring of targets. Herein, we offer a review of the latest developments in the design of LC droplet-based biosensors for qualitative target monitoring and quantitative target analysis.

State-of-the-Art Development in Liquid Crystal Biochemical Sensors

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.

Utility of SPR technology in biotherapeutic development: Qualification for intended use

Surface plasmon resonance (SPR) analysis provides important binding characteristic information for an antibody to its binding partner, such as binding specificity and affinity (K_D). In recent years, SPR has been increasingly used in biosimilar development as part of the comparative analytical similarity assessment. Although there is no systematic study describing how to qualify SPR assays, there are various SPR result types (outputs) that have been used for assay qualification in publicly available regulatory documents. The mixed usage of SPR output can cause confusion and can be misleading when comparing binding attributes among antibody molecules. In this report, using a recombinant huIgG1 (mAb 1) antibody as an example, we performed assay qualification strictly based on the nature of the biomolecular interaction. We recommend that K_D should be used as the output of assay qualification when the K_D can be measured accurately by SPR. When K_D cannot be accurately determined in a SPR setting, sensorgram comparison and Parallel Line Analysis (PLA) can be used to qualify the assay. We emphasize the importance of setting up appropriate SPR assay conditions for target and/or Fc receptor interactions to ensure the assay qualification parameters, such as accuracy and repeatability, to meet the criteria acceptable for regulatory filings. With increasing numbers of biotherapeutics being developed, the methods and guidelines provided here can help to align SPR application between the drug development industry and regulatory authorities which will benefit the scientific communities involved in biotherapeutic drug development.

Next Generation Strategy for Tuning the Thermoresponsive Properties of Micellar and Hydrogel Drug Delivery Vehicles Using Ionic Liquids

Amongst the greatest challenges in developing injectable controlled thermoresponsive micellar and hydrogel drug delivery vehicles include tuning the cloud point (CP) and reducing the gelation temperature (Tgel), below 37 °C,...

Metal-enhanced sensing platform for the highly sensitive detection of C-reactive protein antibody and rhodamine B with applications in cardiovascular diseases and food safety

The potential applications of metal-enhanced fluorescence (MEF) devices include biosensors for the detection of trace amounts in biosciences, biotechnology, and pathogens that are relevant to medical diagnostics and food control. In the present study, the silver (Ag) film thickness (56 nm) of an MEF system was calibrated to maximize the depth-to-width ratio (Γ) of the surface plasmon resonance (SPR) active metal from reflectance dip curves. Upon plasmon coupling with thermally evaporated Ag, we demonstrated a 2.21-fold enhancement compared to the pristine flat substrate with the coefficient of variation (CV) ≈0.22% and the limit of detection (LOD) 0.001 mg L-1 of the concentration of an Alexa Fluor 488-labeled anti-C-reactive protein antibody (CRP@Alexa fluor 488). The structure was developed to simplify the in situ generation of biosensors for the surface-enhanced Raman spectroscopy (SERS) to determine Rhodamine B (RhB) with a highly robust performance. The procedure presented a simple and rapid sample pretreatment for the determination of RhB with a limit of quantification of 10-10 M and a satisfactory linear response (0.98). The results showed the excellent performance of the surface plasmon coupled emission (SPCE), which opens up possibilities for the accurate detection of small-volume and low-concentration target analytes due to the improved sensitivity and signal-to-noise ratio (SNR).

Applications of liquid crystals in biosensing

Liquid crystals (LCs), as a promising branch of highly-sensitive, quick-response, and low-cost materials, are widely applied to the detection of weak external stimuli and have attracted significant attention. Over the past decade, many research groups have been devoted to developing LC-based biosensors due to their self-assembly potential and functional diversity. In this paper, recent investigations on the design and application of LC-based biosensors are reviewed, based on the phenomenon that the orientation of LCs can be directly influenced by the interactions between biomolecules and LC molecules. The sensing principle of LC-based biosensors, as well as their signal detection by probing interfacial interactions, is described to convert, amplify, and quantify the information from targets into optical and electrical parameters. Furthermore, commonly-used LC biosensing targets are introduced, including glucose, proteins, enzymes, nucleic acids, cells, microorganisms, ions, and other micromolecules that are critical to human health. Due to their self-assembly potential, chemical diversity, and high sensitivity, it has been reported that tunable stimuli-responsive LC biosensors show bright perspectives and high superiorities in biological applications. Finally, challenges and future prospects are discussed for the fabrication and application of LC biosensors to both enhance their performance and to realize their promise in the biosensing industry.

Bioresponsive microlasers with tunable lasing wavelength

Lasing particles are emerging tools for amplifying light-matter interactions at the biointerface by exploiting its strong intensity and miniaturized size. Recent advances in implementing laser particles into living cells and tissues have opened a new frontier in biological imaging, monitoring, and tracking. Despite remarkable progress in micro- and nanolasers, lasing particles with surface functionality remain challenging due to the low mode-volume while maintaining a high Q-factor. Herein, we report the novel concept of bioresponsive microlasers by exploiting interfacial energy transfer based on whispering-gallery-mode (WGM) microdroplet cavities. Lasing wavelengths were manipulated by energy transfer-induced changes of a gain spectrum resulting from the binding molecular concentrations at the cavity surface. Both protein-based and enzymatic-based interactions were demonstrated, shedding light on the development of functional microlasers. Finally, tunable lasing wavelengths over a broad spectral range were achieved by selecting different donor/acceptor pairs. This study not only opens new avenues for biodetection, but also provides deep insights into how molecules modulate laser light at the biointerface, laying the foundation for the development of smart bio-photonic devices at the molecular level.

Bio-electrostatic sensitive droplet lasers for molecular detection

Electrostatics plays a critical function in most biomolecules, therefore monitoring molecular electrostatic interactions at the biointerface can provide the basis in diagnosis and biomedical science. Herein we report a bioelectrostatic responsive microlaser based on liquid crystal (LC) droplets and explored its application for the ultrasensitive detection of negatively charged biomolecules. A whispering gallery mode (WGM) laser from positively charged LC microdroplets was designed as the optical resonator, in which the lasing wavelength shift was employed as the sensing parameter. We verified that molecular electrostatic changes at the biointerface of the droplet trigger a wavelength shift in laser spectra. Compared to a conventional polarized optical microscope, a significantly improved sensitivity and dynamic range by four orders of magnitude were achieved. Our results helped discover that the surface-to-volume ratio plays a critical role in the detection sensitivity in WGM laser-based microsensors. Finally, bovine serum albumin and specific biosensing were exploited to demonstrate the potential applications of microlasers with a detection limit in the order of 1 pM, thus offering new alternatives for ultrasensitive label-free biosensing and monitoring of molecular interactions.

Low-fouling and highly sensitive fluorescence immunoassay of protein in serum based on the antifouling magnetic beads

Aim: A low-fouling and highly sensitive fluorescence immunoassay for protein detection in serum was proposed, and IgG was used as a model protein. Materials & methods: SH-PEG-NH2 serving as antifouling coating was conjugated with carboxyl Fe3O4 nanoparticles, and then, the thiol groups were conjugated with antibody via the covalent binding. IgG was captured through magnetic immunoreaction. Highly fluorescent quantum dots modified with streptavidin (SA-QDs) were united with biotin modified IgG antibody to form the sandwich structure. Results & conclusion: The fluorescence immunoassay was able to detect IgG with a detection limit of 3.89 ng/ml in buffer and 5.0 ng/ml in serum with satisfying selectivity and acceptable reproducibility, which demonstrated its potential application in quantitative analysis of real patient serum samples.