Gold nanorods-based lateral flow biosensors for sensitive detection of nucleic acids

Sensitization Strategies of Lateral Flow Immunochromatography for Gold Modified Nanomaterials in Biosensor Development

Gold nanomaterials have become very attractive nanomaterials for biomedical research due to their unique physical and chemical properties, including size dependent optical, magnetic and catalytic properties, surface plasmon resonance (SPR), biological affinity and structural suitability. The performance of biosensing and biodiagnosis can be significantly improved in sensitivity, specificity, speed, contrast, resolution and so on by utilizing multiple optical properties of different gold nanostructures. Lateral flow immunochromatographic assay (LFIA) based on gold nanoparticles (GNPs) has the advantages of simple, fast operation, stable technology, and low cost, making it one of the most widely used in vitro diagnostics (IVDs). However, the traditional colloidal gold (CG)-based LFIA can only achieve qualitative or semi-quantitative detection, and its low detection sensitivity cannot meet the current detection needs. Due to the strong dependence of the optical properties of gold nanomaterials on their shape and surface properties, gold-based nanomaterial modification has brought new possibilities to the IVDs: people have attempted to change the morphology and size of gold nanomaterials themselves or hybrid with other elements for application in LFIA. In this paper, many well-designed plasmonic gold nanostructures for further improving the sensitivity and signal output stability of LFIA have been summarized. In addition, some opportunities and challenges that gold-based LFIA may encounter at present or in the future are also mentioned in this paper. In summary, this paper will demonstrate some feasible strategies for the manufacture of potential gold-based nanobiosensors of post of care testing (POCT) for faster detection and more accurate disease diagnosis.

A wash-free, elution-free and low protein adsorption paper-based material for nucleic acid extraction

Nucleic acid detection technologies have been widely utilized for various diseases. Conventional laboratory tests are less suitable for use in resource-limited settings as they are time-consuming, high-cost, complex, and heavily dependent on benchtop equipment. Rapid nucleic acid detection methods that consist of rapid nucleic acid extraction steps could overcome these challenges. A paper-based platform has been utilized to develop various rapid nucleic acid extraction methods owing to its cost-effectiveness, portability, and easy-modification. However, the existing paper-based nucleic acid extraction technologies mainly focus on improving the adsorption capacity of nucleic acids without reducing the non-specific adsorption capacity of proteins. In this study, paper-based nucleic acid extraction technology with wash-free, elution-free, and low protein adsorption was developed. The fabrication of paper involves the mixing of polyethylene glycol (PEG)-modified cotton fiber, chitosan (COS)-modified cotton fiber, and cotton fiber to form PEG-modified cotton fiber/chitosan-modified cotton fiber/cotton fiber (PEG-CF/COS-CF/CF) paper by the wet molding method. The result showed that PEG-CF/COS-CF/CF paper has a desirable pore size (23.9 ± 4.03 μm), good mechanical strength (dry: 9.37 Mpa and wet: 0.28 Mpa), and hydrophilicity (contact angle: 42.6° ± 0.36°). NH₃⁺ groups of COS and OH^- groups of PEG were observed on its surface and the adsorption efficiency of nucleic acid in TE buffer was 42.48% ± 0.30%. The limit of detection of pure DNA with this PEG-CF/COS-CF/CF paper by qPCR was as low as 25 ng. Additionally, this platform could successfully extract nucleic acid from 30 μL of a saliva sample, highlighting its potential use for clinical sample testing. The proposed paper-based nucleic acid extraction platform shows tremendous potential for disease diagnosis in resource-limited settings.

Comparison of DNA-Gold Nanoparticle Conjugation Methods: Application in Lateral Flow Nucleic Acid Biosensors

Lateral flow nucleic acid biosensors (LFNABs) have attracted extensive attention due to their rapid turnaround time, low cost, and results that are visible to the naked eye. One of the key steps to develop LFNABs is to prepare DNA-gold nanoparticle (DNA-AuNP) conjugates, which affect the sensitivity of LFNABs significantly. To date, various conjugation methods-including the salt-aging method, microwave-assisted dry heating method, freeze-thaw method, low-pH method, and butanol dehydration method-have been reported to prepare DNA-AuNP conjugates. In this study, we conducted a comparative analysis of the analytical performances of LFNABs prepared with the above five conjugation methods, and we found that the butanol dehydration method gave the lowest detection limit. After systematic optimization, the LFNAB prepared with the butanol dehydration method had a detection limit of 5 pM for single-strand DNA, which is 100 times lower than that of the salt-aging method. The as-prepared LFNAB was applied to detect miRNA-21 in human serum, with satisfactory results. The butanol dehydration method thus offers a rapid conjugation approach to prepare DNA-AuNP conjugates for LFNABs, and it can also be extended to other types of DNA biosensors and biomedical applications.

AuPt nanoalloy with dual functionalities for sensitive detection of HPV16 DNA

Human papillomavirus type 16 (HPV16), one of the high-risk types, is responsible for 53% of cervical cancers. The development of an early diagnostic approach with high sensitivity, low-cost, point-of-care testing (POCT) for HPV16 is urgent. In our work, a novel dual-functional AuPt nanoalloy-based lateral flow nucleic acid biosensor (AuPt nanoalloy-based LFNAB) was established with excellent sensitivity for detecting HPV16 DNA for the first time. The AuPt nanoalloy particles were prepared by a one-step reduction method, which was simple, rapid, and green. The AuPt nanoalloy particles retained the performance of initial Au nanoparticles owing to the catalytic activity enabled by Pt. Such dual-functionalities offered two kinds of detection alternatives (i.e., normal mode and amplification mode, respectively). The former is produced just by the black color from the AuPt nanoalloy material itself, and the latter is more color sensitive from its superior catalytic activity. The optimized AuPt nanoalloy-based LFNAB exhibited satisfactory quantitative ability in detecting the target HPV16 DNA in the range of 5-200 pM with a LOD of 0.8 pM at the "amplification mode". The proposed dual-functional AuPt nanoalloy-based LFNAB displayed great potential and promising opportunity in POCT clinical diagnostics.

Rapid on-site nucleic acid testing: On-chip sample preparation, amplification, and detection, and their integration into all-in-one systems

As nucleic acid testing is playing a vital role in increasingly many research fields, the need for rapid on-site testing methods is also increasing. The test procedure often consists of three steps: Sample preparation, amplification, and detection. This review covers recent advances in on-chip methods for each of these three steps and explains the principles underlying related methods. The sample preparation process is further divided into cell lysis and nucleic acid purification, and methods for the integration of these two steps on a single chip are discussed. Under amplification, on-chip studies based on PCR and isothermal amplification are covered. Three isothermal amplification methods reported to have good resistance to PCR inhibitors are selected for discussion due to their potential for use in direct amplification. Chip designs and novel strategies employed to achieve rapid extraction/amplification with satisfactory efficiency are discussed. Four detection methods providing rapid responses (fluorescent, optical, and electrochemical detection methods, plus lateral flow assay) are evaluated for their potential in rapid on-site detection. In the final section, we discuss strategies to improve the speed of the entire procedure and to integrate all three steps onto a single chip; we also comment on recent advances, and on obstacles to reducing the cost of chip manufacture and achieving mass production. We conclude that future trends will focus on effective nucleic acid extraction via combined methods and direct amplification via isothermal methods.

Advances in upconversion luminescence nanomaterial-based biosensor for virus diagnosis

Various infectious viruses have been posing a major threat to global public health, especially SARS-CoV-2, which has already claimed more than six million lives up to now. Tremendous efforts have been made to develop effective techniques for rapid and reliable pathogen detection. The unique characteristics of upconversion nanoparticles (UCNPs) pose numerous advantages when employed in biosensors, and they are a promising candidate for virus detection. Herein, this Review will discuss the recent advancement in the UCNP-based biosensors for virus and biomarkers detection. We summarize four basic principles that guide the design of UCNP-based biosensors, which are utilized with luminescent or electric responses as output signals. These strategies under fundamental mechanisms facilitate the enhancement of the sensitivity of UCNP-based biosensors. Moreover, a detailed discussion and benefits of applying UCNP in various virus bioassays will be presented. We will also address some obstacles in these detection techniques and suggest routes for progress in the field. These progressions will undoubtedly pose UCNP-based biosensors in a prominent position for providing a convenient, alternative approach to virus detection.

Simultaneous electrochemical detection of guanine and adenine using reduced graphene oxide decorated with AuPt nanoclusters

A rapid and sensitive electrochemical sensing platform is reported based on bimetallic gold-platinum nanoclusters (AuPtNCs) dispersed on reduced graphene oxide (rGO) for the simultaneous detection of guanine and adenine using square wave voltammetry (SWV). The synthesis of AuPtNCs-rGO nanocomposite was achieved by a simultaneous reduction of graphene oxide (GO) and metal ions (Au³⁺ and Pt⁴⁺) in an aqueous solution. The developed AuPtNCs-rGO electrochemical sensor with the optimized 50:50 bimetallic (Au:Pt) nanoclusters exhibited an outstanding electrocatalytic performance towards the simultaneous oxidation of guanine and adenine without the aid of any enzymes or mediators in physiological pH. The electrochemical sensor platform showed low detection limits of 60 nM and 100 nM (S/N = 3) for guanine and adenine, respectively, with high sensitivity and an extensive linear range from 1.0 μM to 0.2 mM for both guanine and adenine. The interference from the most common electrochemically active interferents, including ascorbic acid, uric acid, and dopamine, was almost negligible. The simultaneous sensing of guanine and adenine in denatured Salmon Sperm DNA sample was successfully achieved using the proposed platform, showing that the AuPtNCs-rGO nanocomposite could provide auspicious clinical diagnosis and biomedical applications.