Development of liquid crystal biosensor for the detection of amyloid beta-42 levels associated with Alzheimer's disease

Biomarkers in Alzheimer's disease

Alzheimer's disease (AD) is among the most common neurodegenerative disorders. AD is characterized by deposition of neurofibrillary tangles and amyloid plaques, leading to associated secondary pathologies, progressive neurodegeneration, and eventually death. Currently used diagnostics are largely image-based, lack accuracy and do not detect early disease, ie, prior to onset of symptoms, thus limiting treatment options and outcomes. Although biomarkers such as amyloid-β and tau protein in cerebrospinal fluid have gained much attention, these are generally limited to disease progression. Unfortunately, identification of biomarkers for early and accurate diagnosis remains a challenge. As such, body fluids such as sweat, serum, saliva, mucosa, tears, and urine are under investigation as alternative sources for biomarkers that can aid in early disease detection. This review focuses on biomarkers identified through proteomics in various biofluids and their potential for early and accurate diagnosis of AD.

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.

A new ITO-based Aβ42 biosensor for early detection of Alzheimer's disease

In this study, a novel label-free impedimetric immunosensor was fabricated for rapid, selective, and sensitive quantitative analysis of Aβ₄₂ protein for use in the diagnosis of Alzheimer's disease. The immunosensor was fabricated using inexpensive and disposable indium tin oxide polyethylene terephthalate (ITO-PET) electrodes. After the electrodes were modified with 3-glycidoxypropyldimethoxymethylsilane (GPDMMS), the antibody specific to the Aβ₄₂ protein (anti-Aβ₄₂) was immobilized. The affinity interaction between anti-Aβ₄₂ and Aβ₄₂ in the immobilization steps in immunosensor fabrication and in the quantitation of Aβ₄₂ were analyzed using Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV) techniques. Additionally, the morphological changes occurring on the electrode surface during each immobilization step were imaged using scanning electron microscopy (SEM). The linear detection range of the immunosensor was determined as 1-100 pg/mL with the limit of detection value of 0.37 pg/mL. Analytical properties of the biosensor, including reproducibility, repeatability, storage stability, selectivity, and regeneration were investigated. The kinetic behavior of antibody-antigen complex formation was determined for the first time using single frequency impedance (SFI) analysis on an Aβ₄₂ biosensor. The potential for use of the immunosensor in clinical studies was demonstrated by analysis of Aβ₄₂ in commercially purchased human serum.

Liquid crystal-assisted optical biosensor for early-stage diagnosis of mammary glands using HER-2

Breast cancer (BC) is one of the most commonly diagnosed cancers and the second leading cause of cancer mortality among women around the world. The purpose of this study is to present a non-labeled liquid crystal (LC) biosensor, based on the inherent feature of nematic LCs, for the evaluation of BC using the human epidermal growth factor receptor-2 (HER-2) biomarker. The mechanism of this sensing is supported by surface modification with dimethyloctadecyl [3-(trimethoxysilyl) propyl] ammonium chloride (DMOAP) encouraging the long alkyl chains that induce a homeotropic orientation of the LC molecules at the interface. To enhance the binding efficacy of more HER-2 antibody (Ab) on LC aligning agents, a simple ultraviolet radiation-assisted method was also used to increase functional groups on the DMOAP coated slides, thereby improving binding affinity and efficiency onto HER-2 Abs. The designed biosensor makes use of the specific binding of HER-2 protein to HER-2 Ab and disruption of the orientation of LCs. This orientation change leads to a transition of the optical appearance from dark to birefringent, enabling the detection of HER-2. This novel biosensor exhibits a linear optical response to HER-2 concentration in the wide dynamic range of 10^-6-10² ng/mL, with an ultra-low detection limit of 1 fg/mL. As a proof of concept, the designed LC biosensor was successfully investigated for the quantification of HER-2 protein in patients suffering from BC. Owing to the sensitivity, selectivity, and label-free detection, this biosensor may amplify the application of LC-based biosensors for the detection of most types of cancers.

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.

Biosensor approaches on the diagnosis of neurodegenerative diseases: Sensing the past to the future

Early diagnosis of neurodegeneration-oriented diseases that develop with the aging world is essential for improving the patient's living conditions as well as the treatment of the disease. Alzheimer's and Parkinson's diseases are prominent examples of neurodegeneration characterized by dementia leading to the death of nerve cells. The clinical diagnosis of these diseases only after the symptoms appear, delays the treatment process. Detection of biomarkers, which are distinctive molecules in biological fluids, involved in neurodegeneration processes, has the potential to allow early diagnosis of neurodegenerative diseases. Studies on biosensors, whose main responsibility is to detect the target analyte with high specificity, has gained momentum in recent years with the aim of high detection of potential biomarkers of neurodegeneration process. This study aims to provide an overview of neuro-biosensors developed on the basis of biomarkers identified in biological fluids for the diagnosis of neurodegenerative diseases such as Alzheimer's disease (AD), and Parkinson's disease (PD), and to provide an overview of the urgent needs in this field, emphasizing the importance of early diagnosis in the general lines of the neurodegeneration pathway. In this review, biosensor systems developed for the detection of biomarkers of neurodegenerative diseases, especially in the last 5 years, are discussed.

A self-oriented beacon liquid crystal assay for kanamycin detection with AuNPs signal enhancement

The authors report a self-oriented beacon liquid crystal (LC) biosensor for kanamycin (Kana) detection with gold nanoparticle (AuNPs) signal enhancement. In this study, an assay was proposed for Kana detection using the aptamer as a self-oriented beacon. Without an additional orientation agent, the Kana aptamer was used as a self-oriented beacon both as an orientation agent for the LCs and as a signal recognition probe for biological molecules. Gold nanoparticles are blended with desired concentrations of the target molecules, which can greatly improve the performance of the biosensor. In the presence of Kana, AuNPs-Kana-aptamer conjugates will form on the sensing interface of the biosensor, which can remarkably destroy the orientated arrangement of the LCs, resulting in changes in the corresponding polarized images of the LCs. The limit of Kana detection is as low as 0.1 pmol L^-1. It is important to note that the self-oriented beacons are immobilized on the assembled film of the glass slides for the specific recognition of Kana, simultaneously allowing the homeotropic orientation of the LCs. This study also provides a mechanism for the self-orientation beacon and liquid crystal biosensing.