Vertical Nanowire Electrode Arrays as Novel Electrochemical Label-Free Immunosensors

The Evaluation of Clinical Applications for the Detection of the Alzheimer's Disease Biomarker GFAP

One of the most prevalent neurodegenerative diseases is Alzheimer's disease (AD). The hallmarks of AD include the accumulation of amyloid plaques and neurofibrillary tangles, which cause related secondary diseases, progressive neurodegeneration, and ultimately death. The most prevalent cell type in the human central nervous system, astrocytes, are crucial for controlling neuronal function. Glial fibrillary acidic protein (GFAP) is released from tissue into the bloodstream due to astrocyte breakdown in neurological diseases. Increased levels of GFAP in the serum can function as blood markers and be an effective prognostic indicator to help diagnose neurological conditions early on, from stroke to neurodegenerative diseases. The human central nervous system (CNS) is greatly affected by diseases associated with blood GFAP levels. These include multiple sclerosis, intracerebral hemorrhage, glioblastoma multiforme, traumatic brain injuries, and neuromyelitis optica. GFAP demonstrates a strong diagnostic capacity for projecting outcomes following an injury. Furthermore, the increased ability to identify GFAP protein fragments helps facilitate treatment, as it allows continuous screening of CNS injuries and early identification of potential recurrences. GFAP has recently gained attention due to data showing that the plasma biomarker is effective in identifying AD pathology. AD accounts for 60-70% of the approximately 50 million people with dementia worldwide. It is critical to develop molecular markers for AD, whose number is expected to increase to about 3 times and affect humans by 2050, and to investigate possible targets to confirm their effectiveness in the early diagnosis of AD. In addition, most diagnostic methods currently used are image-based and do not detect early disease, i.e. before symptoms appear; thus, treatment options and outcomes are limited. Therefore, recently developed methods such as point-of-care (POC), on-site applications, and enzyme-linked immunosorbent assay-polymerase chain reaction (ELISA-PCR) that provide both faster and more accurate results are gaining importance. This systematic review summarizes published studies with different approaches such as immunosensor, lateral flow, POC, ELISA-PCR, and molecularly imprinted polymer using GFAP, a potential blood biomarker to detect neurological disorders. Here, we also provide an overview of current approaches, analysis methods, and different future detection strategies for GFAP, the most popular biosensing field.

Two-channel electrochemical immunosensor based on one-step-synthesized AuPt-boron-doped graphene electrode for CA153 detection

Herein, a novel dual-channel electrochemical immunosensor was fabricated via vertical growth of AuPt-decorated boron-doped graphene (AuPt-BG) nanosheets as a signal amplification platform to detect cancer antigen 153 (CA153). Highly open, porous AuPt-BG films were synthesized using one-step electron-assisted hot-filament chemical vapor deposition. The Au-Pt alloy nanoparticles were dispersed on BG nanosheets to improve their biocompatibility, and antibodies (Ab) were directly bonded to the AuPt-BG electrode. The architectures enlarged the loading of CA153Ab and efficiently catalyzed the Fe(CN)₆^3-/4- reaction, ultimately amplifying the signals. This novel strategy allows the simultaneous detection of CA153 in the oxidation and reduction channels, improving the reliability of the detection results. The AuPt-BG-based immunosensor exhibited a lower detection limit (0.0012 mU mL^-1, S/N = 3) and wider linear range (0.1-4 × 10⁴ mU mL^-1) along with improved reproducibility, selectivity, and stability for the assay of CA153. Owing to the high process controllability of AuPt-BG films, a large-area electrode for in-vitro analyses and a flexible microelectrode for in-vivo analyses were prepared, which confirmed that the AuPt-BG-based sensor is an ideal CA153 detection platform for clinical diagnosis and practical applications.

Antibody-Antimicrobial Conjugates for Combating Antibiotic Resistance

As the development of new antibiotics lags far behind the emergence of drug-resistant bacteria, alternative strategies to resolve this dilemma are urgently required. Antibody-drug conjugate is a promising therapeutic platform to delivering cytotoxic payloads precisely to target cells for efficient disease treatment. Antibody-antimicrobial conjugates (AACs) have recently attracted considerable interest from researchers as they can target bacteria in the target sites and improve the effectiveness of drugs (i.e., reduced drug dosage and adverse effects), abating the upsurge of antimicrobial resistance. In this review, the selection and progress of three essential blocks that compose the AACs: antibodies, antimicrobial payloads, and linkers are discussed. The commonly used conjugation strategies and the latest applications of AACs in recent years are also summarized. The challenges and opportunities of this booming technology are also discussed at the end of this review.

New immunoprobe: Dual-labeling ZIF-8 embellished with multifunctional bovine serum albumin lamella for electrochemical immunoassay of tumor marker

A new immunoprobe, which can initiate the sedimentation of Ag nanoparticles (NPs) on an electrode surface, was developed for the electrochemical detection of carbohydrate antigen 72-4 (CA 72-4). To design the immunoprobe, zeolitic imidazolate frameworks (ZIFs) were employed as the carrier to enrich thionine molecules, then bovine serum albumin (BSA) was modified on the electrode surface. Advantageously, BSA, served as an anchor to further attach the labeling antibodies (Ab₂) and alkaline phosphatase (ALP) to also be modified on the surface through covalent bonding. To construct the immunosensor, multiwalled carbon nanotube-graphene oxide composites were employed to provide active sites, and the electrodeposited Au NPs were used to immobilize coating antibodies. In the presence of CA 72-4, a sandwich immunosensor was established, and a cascade reaction was initiated to deposit Ag NPs under the catalysis, which can further improve the conductivity of electrode interface. Under the optimal conditions, the immunosensor displayed excellent performance with a wide linear range from 1 μU mL^-1 to 10 U mL^-1 and an ultralow detection limit of 0.438 μU mL^-1 (S/N = 3).

Self-Organized Nanostructure Modified Microelectrode for Sensitive Electrochemical Glutamate Detection in Stem Cells-Derived Brain Organoids

Neurons release neurotransmitters such as glutamate to communicate with each other and to coordinate brain functioning. As increased glutamate release is indicative of neuronal maturation and activity, a system that can measure glutamate levels over time within the same tissue and/or culture system is highly advantageous for neurodevelopmental investigation. To address such challenges, we develop for the first time a convenient method to realize functionalized borosilicate glass capillaries with nanostructured texture as an electrochemical biosensor to detect glutamate release from cerebral organoids generated from human embryonic stem cells (hESC) that mimic various brain regions. The biosensor shows a clear catalytic activity toward the oxidation of glutamate with a sensitivity of 93 ± 9.5 nA·µM-1·cm-2. It was found that the enzyme-modified microelectrodes can detect glutamate in a wide linear range from 5 µM to 0.5 mM with a limit of detection (LOD) down to 5.6 ± 0.2 µM. Measurements were performed within the organoids at different time points and consistent results were obtained. This data demonstrates the reliability of the biosensor as well as its usefulness in measuring glutamate levels across time within the same culture system.

Clinically Relevant Detection of Streptococcus pneumoniae with DNA-Antibody Nanostructures

Streptococcus pneumoniae (SP) is a pathogenic bacterium and a major cause of community-acquired pneumonia that could be fatal if left untreated. Therefore, rapid and sensitive detection of SP is crucial to enable targeted treatment during SP infections. In this study, DNA tetrahedron (DNA TH) with a hollow structure is anchored on gold electrodes to construct an electrochemical immunosensor for rapid detection of pneumococcal surface protein A (PspA) peptide and SP lysate from synthetic and actual human samples. This DNA nanostructure-based immunosensor displays excellent electrochemical activity toward PspA with a sensitive linear region from 0 to 8 ng/mL of PspA peptide and a low limit of detection (LOD) of 0.218 ng/mL. In addition, this DNA-TH-based immunosensor exhibits good sensing performance toward SP lysate in a clinically relevant linear range from 5 to 100 CFU/mL with a LOD of 0.093 CFU/mL. Along with these attractive features, this electrochemical immunosensor is able to specifically recognize and detect the PspA peptide mixed with other physiologically relevant components like bovine serum albumin (BSA) and lipopolysaccharide. In addition, our sensor could detect SP lysate even when dispersed in BSA or Escherichia coli lysate. Lastly, uncultured samples from the nasal cavity, mouth, and axilla of a human subject could be successfully determined by this well-designed electrochemical immunosensor.

A Label-Free, Quantitative Fecal Hemoglobin Detection Platform for Colorectal Cancer Screening

The early detection of colorectal cancer is vital for disease management and patient survival. Fecal hemoglobin detection is a widely-adopted method for screening and early diagnosis. Fecal Immunochemical Test (FIT) is favored over the older generation chemical based Fecal Occult Blood Test (FOBT) as it does not require dietary or drug restrictions, and is specific to human blood from the lower digestive tract. To date, no quantitative FIT platforms are available for use in the point-of-care setting. Here, we report proof of principle data of a novel low cost quantitative fecal immunochemical-based biosensor platform that may be further developed into a point-of-care test in low-resource settings. The label-free prototype has a lower limit of detection (LOD) of 10 µg hemoglobin per gram (Hb/g) of feces, comparable to that of conventional laboratory based quantitative FIT diagnostic systems.

Lab on a chip sensor for rapid detection and antibiotic resistance determination of Staphylococcus aureus

The Gram-positive bacterium, Staphylococcus aureus (S. aureus), is a major pathogen responsible for a variety of infectious diseases ranging from cellulitis to more serious conditions such as septic arthritis and septicaemia. Timely treatment with appropriate antibiotic therapy is essential to ensure clinical defervescence and to prevent further complications such as infective endocarditis or organ impairment due to septic shock. To date, initial antibiotic choice is empirical, using a "best guess" of likely organism and sensitivity- an approach adopted due to the lack of rapid identification methods for bacteria. Current culture based methods take up to 5 days to identify the causative bacterial pathogen and its antibiotic sensitivity. This paper provides proof of concept for a biosensor, based on interdigitated electrodes, to detect the presence of S. aureus and ascertain its sensitivity to flucloxacillin rapidly (within 2 hours) in a cost effective manner. The proposed method is label-free and uses non-faradic measurements. This is the first study to successfully employ interdigitated electrodes for the rapid detection of antibiotic resistance. The method described has important potential outcomes of faster definitive antibiotic treatment and more rapid clinical response to treatment.

Two-dimensional graphitic carbon nitride nanosheets for biosensing applications

Two-dimensional graphitic carbon nitride nanosheets (CNNSs) with planar graphene-like structure have stimulated increasingly research interest in recent years due to their unique physicochemical properties. CNNSs possess superior stability, high fluorescence quantum yield, low-toxicity, excellent biocompatibility, unique electroluminescent and photoelectrochemical properties, which make them appropriate candidates for biosensing. In this review, we first introduce the preparation and unique properties of CNNSs, with emphasis on their superior properties for biosensing. Then, recent advances of CNNSs in photoelectrochemical biosensing, electrochemiluminescence biosensing and fluorescence biosensing are highlighted. An additional attention is paid to the marriage of CNNSs and nucleic acids, which exhibits great potentials in both biosensing and intracellular imaging. Finally, current challenges and opportunities of this 2D material are outlined. Inspired by the unique properties of CNNSs and their advantages in biological applications, we expect that more attention will be drawn to this promising 2D material and extensive applications can be found in bioanalysis and diseases diagnosis.

Three Dimensional Sculpturing of Vertical Nanowire Arrays by Conventional Photolithography

Ordered nanoarchitectures have attracted an intense research interest recently because of their promising device applications. They are always fabricated by self-assembling building blocks such as nanowires, nanodots. This kind of bottom up approaches is limited in poor control over height, lateral resolution, aspect ratio, and patterning. Here, we break these limits and realize 3D sculpturing of vertical ZnO nanowire arrays (NAs) based on the conventional photolithography approach. These are achieved by immersing nanowire NAs in thick photoresist (PR) layers, which enable the cutting and patterning of ZnO NAs as well as the tailoring of NAs. Our strategy of 3D sculpturing of NAs promisingly paves the way for designing novel NAs-based nanoarchitectures.