Homogeneous, Nanoparticle-Based Quantitative Colorimetric Detection of Oligonucleotides

Zika Virus NS1 Protein Detection Using Gold Nanoparticle-Assisted Dynamic Light Scattering

The Zika virus (ZIKV) is a global health threat due to its rapid spread and severe health implications, including congenital abnormalities and neurological complications. Differentiating ZIKV from other arboviruses such as dengue virus (DENV) is crucial for effective diagnosis and treatment. This study presents the development of a biosensor for detecting the ZIKV non-structural protein 1 (NS1) using gold nanoparticles (AuNPs) functionalized with monoclonal antibodies employing dynamic light scattering (DLS). The biosensor named ZINS1-mAb-AuNP exhibited specific binding to the ZIKV NS1 protein, demonstrating high colloidal stability indicated by a hydrodynamic diameter (DH) of 140 nm, detectable via DLS. In the absence of the protein, the high ionic strength medium caused particle aggregation. This detection method showed good sensitivity and specificity, with a limit of detection (LOD) of 0.96 μg mL-1, and avoided cross-reactivity with DENV2 NS1 and SARS-CoV-2 spike proteins. The ZINS1-mAb-AuNP biosensor represents a promising tool for the early and accurate detection of ZIKV, facilitating diagnostic and treatment capabilities for arboviral infections.

DNA functionalized programmable hybrid biomaterials for targeted multiplexed applications

With the advent of DNA nanotechnology, DNA-based biomaterials have emerged as a unique class of materials at the center of various biological advances. Owing to DNA's high modification capacity via programmable Watson-Crick base-pairing, DNA structures of desired design with increased complexity have been developed. However, the limited scalability, along with poor mechanical properties, high synthesis costs, and poor stability, reduced the adaptability of DNA-based materials to complex biological applications. DNA-based hybrid biomaterials were designed to overcome these limitations by conjugating DNA with functional materials. Today, DNA-based hybrid materials have attracted significant attention in biological engineering with broad application prospects in biomedicine, clinical diagnosis, and nanodevices. Here, we summarize the recent advances in DNA-based hybrid materials with an in-depth understanding of general molecular design principles, functionalities, and applications. Finally, the challenges and prospects associated with DNA-based hybrid materials are discussed at the end of this review.

DNAzyme-RCA-based colorimetric and lateral flow dipstick assays for the point-of-care testing of exosomal m5C-miRNA-21

Methylation of microRNAs (miRNAs) is a post-transcriptional modification that affects miRNA activity by altering the specificity of miRNAs to target mRNAs. Abnormal methylation of miRNAs in cancer suggests their potential as a tumor marker. However, the traditional methylated miRNA detection mainly includes mass spectrometry, sequencing and others; complex procedures and reliance on large instruments greatly limit their application in point-of-care testing (POCT). Based on this, we developed DNAzyme-RCA-based gold nanoparticle (AuNP) colorimetric and lateral flow dipstick (LFD) assays to achieve convenient detection of exosomal 5-methylcytosine miRNA-21 (m5C-miRNA-21) for the first time. The two assays achieved specific recognition and linear amplification of m5C-miRNA-21 through the DNAzyme triggered RCA reaction and color output with low background interference through AuNP aggregation induced by base complementary pairing. The lowest concentration of m5C-miRNA-21 visible to the naked eye of the two assays can reach 1 pM and 0.1 pM, respectively. Detection of exosomal m5C-miRNA-21 in clinical blood samples showed that the expression level of m5C-miRNA-21 in colorectal cancer patients was significantly higher than that in healthy individuals. This approach not only demonstrates a new strategy for the detection of colorectal cancer but also provides a reference for the development of novel diagnostic tools for other miRNA methylation-related diseases.

Optical nanomaterial-based detection of biomarkers in liquid biopsy

Liquid biopsy, which is a minimally invasive procedure as an alternative to tissue biopsy, has been introduced as a new diagnostic/prognostic measure. By screening disease-related markers from the blood or other biofluids, it promises early diagnosis, timely prognostication, and effective treatment of the diseases. However, there will be a long way until its realization due to its conceptual and practical challenges. The biomarkers detected by liquid biopsy, such as circulating tumor cell (CTC) and circulating tumor DNA (ctDNA), are extraordinarily rare and often obscured by an abundance of normal cellular components, necessitating ultra-sensitive and accurate detection methods for the advancement of liquid biopsy techniques. Optical biosensors based on nanomaterials open an important opportunity in liquid biopsy because of their enhanced sensing performance with simple and practical properties. In this review article, we summarized recent innovations in optical nanomaterials to demonstrate the sensitive detection of protein, peptide, ctDNA, miRNA, exosome, and CTCs. Each study prepares the optical nanomaterials with a tailored design to enhance the sensing performance and to meet the requirements of each biomarker. The unique optical characteristics of metallic nanoparticles (NPs), quantum dots, upconversion NPs, silica NPs, polymeric NPs, and carbon nanomaterials are exploited for sensitive detection mechanisms. These recent advances in liquid biopsy using optical nanomaterials give us an opportunity to overcome challenging issues and provide a resource for understanding the unknown characteristics of the biomarkers as well as the mechanism of the disease.

Hydrogel-Based Biosensors for Effective Therapeutics

Nanotechnology and polymer engineering are navigating toward new developments to control and overcome complex problems. In the last few decades, polymer engineering has received researchers' attention and similarly, polymeric network-engineered structures have been vastly studied. Prior to therapeutic application, early and rapid detection analyses are critical. Therefore, developing hydrogel-based sensors to manage the acute expression of diseases and malignancies to devise therapeutic approaches demands advanced nanoengineering. However, nano-therapeutics have emerged as an alternative approach to tackling strenuous diseases. Similarly, sensing applications for multiple kinds of analytes in water-based environments and other media are gaining wide interest. It has also been observed that these functional roles can be used as alternative approaches to the detection of a wide range of biomolecules and pathogenic proteins. Moreover, hydrogels have emerged as a three-dimensional (3D) polymeric network that consists of hydrophilic natural or synthetic polymers with multidimensional dynamics. The resemblance of hydrogels to tissue structure makes them more unique to study inquisitively. Preceding studies have shown a vast spectrum of synthetic and natural polymer applications in the field of biotechnology and molecular diagnostics. This review explores recent studies on synthetic and natural polymers engineered hydrogel-based biosensors and their applications in multipurpose diagnostics and therapeutics. We review the latest studies on hydrogel-engineered biosensors, exclusively DNA-based and DNA hydrogel-fabricated biosensors.

Gold nanoparticles: current and upcoming biomedical applications in sensing, drug, and gene delivery

Gold nanoparticles (AuNPs) present unique physicochemical characteristics, low cytotoxicity, chemical stability, size/morphology tunability, surface functionalization capability, and optical properties which can be exploited for detection applications (colorimetry, surface-enhanced Raman scattering, and photoluminescence). The current challenge for AuNPs is incorporating these properties in developing more sensible and selective sensing methods and multifunctional platforms capable of controlled and precise drug or gene delivery. This review briefly highlights the recent progress of AuNPs in biomedicine as bio-sensors and targeted nano vehicles.

Solution properties of spherical gold nanoparticles with grafted DNA chains from simulation and theory

There has been a rapidly growing interest in the use of functionalized Au nanoparticles (NPs) as platforms in multiple applications in medicine and manufacturing. The sensing and targeting characteristics of these NPs, and the realization of precisely organized structures in manufacturing applications using such NPs, depend on the control of their surface functionalization. NP functionalization typically takes the form of polymer grafted layers, and a detailed knowledge of the chemical and structural properties of these layers is required to molecularly engineer the particle characteristics for specific applications. However, the prediction and experimental determination of these properties to enable the rational engineering of these particles is a persistent problem in the development of this class of materials. To address this situation, molecular dynamic simulations were performed based on a previously established coarse-grained single-stranded DNA (ssDNA) model to determine basic solution properties of model ssDNA-grafted NP-layers under a wide range of conditions. In particular, we emphasize the calculation of the hydrodynamic radius for ssDNA-grafted Au NPs as a function of structural parameters such as ssDNA length, NP core size, and surface coverage. We also numerically estimate the radius of gyration and the intrinsic viscosity of these NPs, which in combination with hydrodynamic radius estimates, provide valuable information about the fluctuating structure of the grafted polymer layers. We may then understand the origin of the commonly reported variation in effective NP "size" by different measurement methods, and then exploit this information in connection to material design and characterization in connection with the ever-growing number of applications utilizing polymer-grafted NPs.

Green Route Synthesis and Characterization Techniques of Silver Nanoparticles and Their Biological Adeptness

The development of the most reliable and green techniques for nanoparticle synthesis is an emerging step in the area of green nanotechnology. Many conventional approaches used for nanoparticle (NP) synthesis are expensive, deadly, and nonenvironmental. In this new era of nanotechnology, to overcome such concerns, natural sources which work as capping and reducing agents, including bacteria, fungi, biopolymers, and plants, are suitable candidates for synthesizing AgNPs. The surface morphology and applications of AgNPs are significantly pretentious to the experimental conditions by which they are synthesized. Available scattered information on the synthesis of AgNPs comprises the influence of altered constraints and characterization methods such as FTIR, UV-vis, DLS, SEM, TEM, XRD, EDX, etc. and their properties and applications. This review focuses on all the above-mentioned natural sources that have been used for AgNP synthesis recently. The green routes to synthesize AgNPs have established effective applications in various areas, including biosensors, magnetic resonance imaging (MRI), cancer treatment, surface-enhanced Raman spectroscopy (SERS), antimicrobial agents, drug delivery, gene therapy, DNA analysis, etc. The existing boundaries and prospects for metal nanoparticle synthesis by the green route are also discussed herein.

Transcription-Based Amplified Colorimetric Thrombin Sensor Using Non-Crosslinking Aggregation of DNA-Modified Gold Nanoparticles

Gold nanoparticles (AuNPs) have been employed as colorimetric biosensors due to the color difference between their dispersed (red) and aggregated (blue) states. Although signal amplification reactions triggered by structural changes of the ligands on AuNPs have been widely used to improve measurement sensitivity, the use of ligands is limited. In this study, we designed a AuNP-based signal-amplifying sandwich biosensor, which does not require a conformational change in the ligands. Thrombin was used as a model target, which is recognized by two different probes. In the presence of the target, an extension reaction occurs as a result of hybridization of the two probes. Then RNA synthesis is started by RNA polymerase activation due to RNA promoter duplex formation. The amplified RNA drives aggregation or dispersion of the AuNPs, and a difference of the color if the AuNP solution is observed. As this detection system does not require a conformational change in the ligand, it can be generically applied to a wide range ligands.

Nanotools for Sepsis Diagnosis and Treatment

Sepsis is one of the leading causes of death worldwide with high mortality rates and a pathological complexity hindering early and accurate diagnosis. Today, laboratory culture tests are the epitome of pathogen recognition in sepsis. However, their consistency remains an issue of controversy with false negative results often observed. Clinically used blood markers, C reactive protein (CRP) and procalcitonin (PCT) are indicators of an acute-phase response and thus lack specificity, offering limited diagnostic efficacy. In addition to poor diagnosis, inefficient drug delivery and the increasing prevalence of antibiotic-resistant microorganisms constitute significant barriers in antibiotic stewardship and impede effective therapy. These challenges have prompted the exploration for alternative strategies that pursue accurate diagnosis and effective treatment. Nanomaterials are examined for both diagnostic and therapeutic purposes in sepsis. The nanoparticle (NP)-enabled capture of sepsis causative agents and/or sepsis biomarkers in biofluids can revolutionize sepsis diagnosis. From the therapeutic point of view, currently existing nanoscale drug delivery systems have proven to be excellent allies in targeted therapy, while many other nanotherapeutic applications are envisioned. Herein, the most relevant applications of nanomedicine for the diagnosis, prognosis, and treatment of sepsis is reviewed, providing a critical assessment of their potentiality for clinical translation.

Development of label-free gold nanoparticle based rapid colorimetric assay for clinical/point-of-care screening of cervical cancer

Cervical cancer is the fourth largest cancer, affecting women across the globe. Rapid screening is of vital importance for diagnosis and treatment of the disease, especially in developing countries with high risk populations. In this paper, we report a simple, novel and rapid approach for qualitative screening of cervical cancer. A label-free colorimetric technique ("C-ColAur") involving the in situ formation of gold nanoparticles (Au NPs) in the presence of clinical samples is demonstrated. The as-formed Au NPs, owing to the sample composition produced a characteristic color that can be used for the qualitative detection of malignancy. We demonstrated the proof of principle using clinical samples (cervical fluid) collected from both cancer affected and healthy individuals. The results of the detection technique, "C-ColAur" when compared with those of the existing conventional diagnostic procedures (i.e. Pap smear or biopsy), showed 96.42% sensitivity. With the detection time less than a minute and with no/minimal sample processing requirements, the proposed technique shows great potential for point-of-care as well as clinical screening of cervical cancer.

Insights into the Formation of DNA-Magnetic Nanoparticle Hybrid Structures: Correlations between Morphological Characterization and Output from Magnetic Biosensor Measurements

Understanding the binding mechanism between probe-functionalized magnetic nanoparticles (MNPs) and DNA targets or amplification products thereof is essential in the optimization of magnetic biosensors for the detection of DNA. Herein, the molecular interaction forming hybrid structures upon hybridization between DNA-functionalized magnetic nanoparticles, exhibiting Brownian relaxation, and rolling circle amplification products (DNA-coils) is investigated by the use of atomic force microscopy in a liquid environment and magnetic biosensors measuring the frequency-dependent magnetic response and the frequency-dependent modulation of light transmission. This approach reveals the qualitative and quantitative correlations between the morphological features of the hybrid structures with their magnetic response. The suppression of the high-frequency peak in the magnetic response and the appearance of a new peak at lower frequencies match the formation of larger sized assemblies upon increasing the concentration of DNA-coils. Furthermore, an increase of the DNA-coil concentration induces an increase in the number of MNPs per hybrid structure. This study provides new insights into the DNA–MNP binding mechanism, and its versatility is of considerable importance for the mechanistic characterization of other DNA-nanoparticle biosensor systems.

Colorimetric Urinalysis for On-Site Detection of Metabolic Biomarkers

Over the past few decades, colorimetric assays have been developed for cost-effective and rapid on-site urinalysis. Most of these assays were employed for detection of biomarkers such as glucose, uric acid, ions, and albumin that are abundant in urine at micromolar to millimolar levels. In contrast, direct assaying of urinary biomarkers such as glycated proteins, low-molecular-weight reactive oxygen species, and nucleic acids that are present at significantly lower levels (nanomolar to picomolar) remain challenging due to the interferences from the urine sample matrix. State-of-the-art assays for detection of trace amounts of urinary biomarkers typically utilize time-consuming and equipment-dependent sample pretreatment or clean-up protocols prior to assaying, which limits their applicability for on-site analysis. Herein, we report a colorimetric assay for on-site detection of trace amount of generic biomarkers in urine without involving tedious sample pretreatment protocols. The detection strategy is based on monitoring the changes in optical properties of poly(3-(4-methyl-3'-thienyloxy)propyltriethylammonium bromide) upon interacting with an aptamer or a peptide nucleic acid in the presence and absence of target biomarkers of relevance for the diagnosis of metabolic complications and diabetes. As a proof of concept, this study demonstrates facile assaying of advanced glycation end products, 8-hydroxy-2'-deoxyguanosine and hepatitis B virus DNA in urine samples at clinically relevant concentrations, with limits of detection of ∼850 pM, ∼650 pM, and ∼ 1 nM, respectively. These analytes represent three distinct classes of biomarkers: (i) glycated proteins, (ii) low-molecular-weight reactive oxygen species, and (iii) nucleic acids. Hence, the proposed methodology is applicable for rapid detection of generic biomarkers in urine, without involving sophisticated equipment and skilled personnel, thereby enabling on-site urinalysis. At the end of the contribution, we discuss the opportunity to translate the homogeneous assay into a paper-based format.

Self-Assembly and Crystallization of DNA-Coated Colloids via Linker-Encoded Interactions

Coating colloidal particles with DNA is a promising strategy to make functional nanoscale materials because the particles can be programmed to spontaneously self-assemble into complex, ordered structures. In this Article, we explore the phase behavior and types of structures that can be formed when interactions between DNA-coated colloids are specified by linker DNA strands dispersed in solution. We show that linker-mediated interactions direct the self-assembly of colloids into equilibrium crystal structures. Furthermore, we demonstrate how different linker sequences and concentrations produce different crystal lattices, whose symmetry and compositional order are encoded exclusively by the linker-mediated interactions. These results illustrate how linkers can be used to separate the assembly instructions, encoded in the linkers, from the colloids themselves. We also examine the phase behavior of asymmetric linkers, which bind more strongly to one colloidal species than the other. We find that asymmetry strongly influences the concentration dependence of the colloidal interactions, which we explain using a mean-field model. We also find evidence that asymmetric linkers might help to reduce kinetic bottlenecks to colloidal crystallization. Together, our findings expand the design rules of linker-mediated self-assembly and make connections between the various schemes for programming assembly of DNA-coated colloids reported in the literature.

Highly sensitive label-free bio-interfacial colorimetric sensor based on silk fibroin-gold nanocomposite for facile detection of chlorpyrifos pesticide

Herein, the preparation of gold nanoparticles-silk fibroin (SF-AuNPs) dispersion and its label-free colorimetric detection of the organophosphate pesticide, namely chlorpyrifos, at ppb level are reported. The silk fibroin solution was extracted from B. mori silk after performing degumming, dissolving and dialysis steps. This fibroin solution was used for synthesis of gold nanoparticles in-situ without using any external reducing and capping agent. X-ray Diffractometry (XRD), Field Emission Transmission Electron Microscopy (FETEM) along with Surface Plasmon Resonance based optical evaluation confirmed generation of gold nanoparticles within SF matrix. The resultant SF-AuNPs dispersion exhibited rapid and excellent colorimetric pesticide sensing response even at 10 ppb concentration. Effect of additional parameters viz. pH, ionic concentration and interference from other pesticide samples was also studied. Notably, SF-AuNPs dispersion exhibited selective colorimetric pesticide sensing response which can be calibrated. Furthermore, this method was extended to various simulated real life samples such as tap water, soil and agricultural products including plant residues to successfully detect the presence of chlorpyrifos pesticide. The proposed colorimetric sensor system is facile yet effective and can be employed by novice rural population and expert researchers alike. It can be exploited as preliminary tool for label-free colorimetric chlorpyrifos pesticide sensing in water and agricultural products.

Perspective on chymotrypsin detection

Chymotrypsin is one of the most extensively known proteases participating in the pathogenesis of various diseases, which can be used in drug discovery and clinical diagnosis.

A Bottom-Up Approach for Developing Aptasensors for Abused Drugs: Biosensors in Forensics

Aptamer-based point-of-care (POC) diagnostics platforms may be of substantial benefit in forensic analysis as they provide rapid, sensitive, user-friendly, and selective analysis tools for detection. Aptasensors have not yet been adapted commercially. However, the significance of the applications of aptasensors in the literature exceeded their potential. Herein, in this review, a bottom-up approach is followed to describe the aptasensor development and application procedure, starting from the synthesis of the corresponding aptamer sequence for the selected analyte to creating a smart surface for the sensitive detection of the molecule of interest. Optical and electrochemical biosensing platforms, which are designed with aptamers as recognition molecules, detecting abused drugs are critically reviewed, and existing and possible applications of different designs are discussed. Several potential disciplines in which aptamer-based biosensing technology can be of greatest value, including forensic drug analysis and biological evidence, are then highlighted to encourage researchers to focus on developing aptasensors in these specific areas.

Gold and silver nanoparticles in resonance Rayleigh scattering techniques for chemical sensing and biosensing: a review

This review (with 116 refs.) summarizes the state of the art in resonance Rayleigh scattering (RRS)-based analytical methods. Following an introduction into the fundamentals of RRS and on the preparation of metal nanoparticles, a first large section covers RRS detection methods based on the use of gold nanoparticles, with subsections on proteins (albumin, bovine serum albumin and ovalbumin, glycoproteins, folate receptors, iron binding-proteins, G-proteins-coupled receptors, transmembrane proteins, epidermal growth factor receptors), on pesticides, saccharides, vitamins, heavy metal ions (such as mercury, silver, chromium), and on cationic dyes. This is followed by a section on RRS methods based on the use of silver nanoparticles, with subsections on the detection of nucleic acids and insecticides. Several Tables are presented where an RRS method is compared to the performance of other methods. A concluding section summarizes the current status, addresses current challenges, and gives an outlook on potential future trends. Graphical Abstract Change in the resonance Rayleigh scattering (RRS) intensity when mixing the nanoparticles with the specific analyte.

Dark-Field Microwells toward High-Throughput Direct miRNA Sensing with Gold Nanoparticles

MicroRNA (miRNA) is a class of short RNA that is emerging as an ideal biomarker, as its expression level has been found to correlate with different types of diseases including diabetes and cancer. The detection of miRNA is highly beneficial for early diagnostics and disease monitoring. However, miRNA sensing remains difficult because of its small size and low expression levels. Common techniques such as quantitative real-time polymerase chain reaction (qRT-PCR), in situ hybridization and Northern blotting have been developed to quantify miRNA in a given sample. Nevertheless, these methods face common challenges in point-of-care practice as they either require complicated sample handling and expensive equipment, or suffer from low sensitivity. Here we present a new tool based on dark-field microwells to overcome these challenges in miRNA sensing. This miniaturized device enables the readout of a gold nanoparticle assay without the need of a dark-field microscope. We demonstrate the feasibility of the dark-field microwells to detect miRNA in both buffer solution and cell lysate. The dark-field microwells allow affordable miRNA sensing at a high throughput which make them a promising tool for point-of-care diagnostics.

The Role of Temperature and Lipid Charge on Intake/Uptake of Cationic Gold Nanoparticles into Lipid Bilayers

Understanding the molecular mechanisms governing nanoparticle-membrane interactions is of prime importance for drug delivery and biomedical applications. Neutron reflectometry (NR) experiments are combined with atomistic and coarse-grained molecular dynamics (MD) simulations to study the interaction between cationic gold nanoparticles (AuNPs) and model lipid membranes composed of a mixture of zwitterionic di-stearoyl-phosphatidylcholine (DSPC) and anionic di-stearoyl-phosphatidylglycerol (DSPG). MD simulations show that the interaction between AuNPs and a pure DSPC lipid bilayer is modulated by a free energy barrier. This can be overcome by increasing temperature, which promotes an irreversible AuNP incorporation into the lipid bilayer. NR experiments confirm the encapsulation of the AuNPs within the lipid bilayer at temperatures around 55 °C. In contrast, the AuNP adsorption is weak and impaired by heating for a DSPC-DSPG (3:1) lipid bilayer. These results demonstrate that both the lipid charge and the temperature play pivotal roles in AuNP-membrane interactions. Furthermore, NR experiments indicate that the (negative) DSPG lipids are associated with lipid extraction upon AuNP adsorption, which is confirmed by coarse-grained MD simulations as a lipid-crawling effect driving further AuNP aggregation. Overall, the obtained detailed molecular view of the interaction mechanisms sheds light on AuNP incorporation and membrane destabilization.

Programmable Atom Equivalents: Atomic Crystallization as a Framework for Synthesizing Nanoparticle Superlattices

Decades of research efforts into atomic crystallization phenomenon have led to a comprehensive understanding of the pathways through which atoms form different crystal structures. With the onset of nanotechnology, methods that use colloidal nanoparticles (NPs) as nanoscale "artificial atoms" to generate hierarchically ordered materials are being developed as an alternative strategy for materials synthesis. However, the assembly mechanisms of NP-based crystals are not always as well-understood as their atomic counterparts. The creation of a tunable nanoscale synthon whose assembly can be explained using the context of extensively examined atomic crystallization will therefore provide significant advancement in nanomaterials synthesis. DNA-grafted NPs have emerged as a strong candidate for such a "programmable atom equivalent" (PAE), because the predictable nature of DNA base-pairing allows for complex yet easily controlled assembly. This Review highlights the characteristics of these PAEs that enable controlled assembly behaviors analogous to atomic phenomena, which allows for rational material design well beyond what can be achieved with other crystallization techniques.

Model-free description of polymer-coated gold nanoparticle dynamics in aqueous solutions obtained by Bayesian analysis of neutron spin echo data

We present a neutron spin echo study of the nanosecond dynamics of polyethylene glycol (PEG) functionalized nanosized gold particles dissolved in D_{2}O at two temperatures and two different PEG molecular weights (400D and 2000D). The analysis of the neutron spin echo data was performed by applying a Bayesian approach to the description of time correlation function decays in terms of exponential terms, recently proved to be theoretically rigorous. This approach, which addresses in a direct way the fundamental issue of model choice in any dynamical analysis, provides here a guide to the most statistically supported way to follow the decay of the intermediate scattering functions I(Q,t) by basing on statistical grounds the choice of the number of terms required for the description of the nanosecond dynamics of the studied systems. Then, the presented analysis avoids from the start resorting to a preselected framework and can be considered as model free. By comparing the results of PEG-coated nanoparticles with those obtained in PEG2000 solutions, we were able to disentangle the translational diffusion of the nanoparticles from the internal dynamics of the polymer grafted to them, and to show that the polymer corona relaxation follows a pure exponential decay in agreement with the behavior predicted by coarse grained molecular dynamics simulations and theoretical models. This methodology has one further advantage: in the presence of a complex dynamical scenario, I(Q,t) is often described in terms of the Kohlrausch-Williams-Watts function that can implicitly represent a distribution of relaxation times. By choosing to describe the I(Q,t) as a sum of exponential functions and with the support of the Bayesian approach, we can explicitly determine when a finer-structure analysis of the dynamical complexity of the system exists according to the available data without the risk of overparametrization. The approach presented here is an effective tool that can be used in general to provide an unbiased interpretation of neutron spin echo data or whenever spectroscopy techniques yield time relaxation data curves.

Fabrication of Metal Nanostructures on DNA Templates

Metal nanoarchitectures fabrication based on DNA assembly has attracted a good deal of attention. DNA nanotechnology enables precise organization of nanoscale objects with extraordinary structural programmability. The spatial addressability of DNA nanostructures and sequence-dependent recognition allow functional elements to be precisely positioned; thus, novel functional materials that are difficult to produce using conventional methods could be fabricated. This review focuses on the recent development of the fabrication strategies toward manipulating the shape and morphology of metal nanoparticles and nanoassemblies based on the rational design of DNA structures. DNA-mediated metallization, including DNA-templated conductive nanowire fabrication and sequence-selective metal deposition, etc., is briefly introduced. The modifications of metal nanoparticles (NPs) with DNA and subsequent construction of heterogeneous metal nanoarchitectures are highlighted. Importantly, DNA-assembled dynamic metal nanostructures that are responsive to different stimuli are also discussed as they allow the design of smart and dynamic materials. Meanwhile, the prospects and challenges of these shape-and morphology-controlled strategies are summarized.

Triplex-hybridizing bioconjugated gold nanoparticles for specific Y-chromosome sequence targeting of bull spermatozoa

Gold nanoparticles (AuNPs) are widely used in biomedical applications for drug targeting and bioimaging. This often neccesitates their functionalization with biomolecules carrying a defined biological function, yielding gold nanoparticle bioconjugates. The utilization of triplex-forming oligonucleotides (TFOs) as ligands gives access to nanoconjugates as tools for specific DNA-related nanotargeting via triplex hybridization. Since triplex hybridization with nanobioconjugates has to date not been shown on biologically relevant samples, sex-specific sperm marking may be an appropriate model system to demonstrate the opportunities of this targeting method in vitro. In this study, we focused on specific labeling of repetitive target sites enriched on the bovine Y-chromosome using triplex forming oligonucleotides. First, the functionality of a specific locked nucleic acid (LNA) sequence was confirmed on bovine free DNA and on demembranated sperm heads. Thereafter, the influence of AuNPs on triplex hybridization was spectrophotometrically analyzed employing synthetic dsDNA, genomic DNA and demembranated sperm heads. Results from the SPR-peak shift indicate that TFO-AuNP hybridize to bovine gDNA in a qualitative and significant manner. These results confirm successful triplex hybridization on biologically relevant target sites as well as the establishment of a method to use gold nanoparticles as a suitable tool for sex-selective hybridization.

MicroRNA sensors based on gold nanoparticles

MicroRNAs (miRNAs) are small regulatory RNAs, the dysregulation of which has been associated with the progression of several human diseases, including cancer. Interestingly, these molecules can be used as biomarkers for early disease diagnosis and can be found in a variety of body fluids and tissue samples. However, their specific properties and very low concentrations make their detection rather challenging. In this regard, current detection methods are complex, cost-ineffective, and of limited application in point-of-care settings or resource-limited facilities. Recently, nanotechnology-based approaches have emerged as promising alternatives to conventional miRNA detection methods and paved the way for research towards sensitive, fast, and low-cost detection systems. In particular, due to their exceptional properties, the use of gold nanoparticles (AuNPs) has significantly improved the performance of miRNA biosensors. This review discusses the application of AuNPs in different miRNA sensor modalities, commenting on recently reported examples. A practical overview of each modality is provided, highlighting their future use in clinical diagnosis. Graphical abstract ᅟ.

Gold core-satellite nanostructure linked by oligonucleotides for detection of glutathione with LSPR scattering spectrum

We demonstrated a sensitive method for detection of glutathione (GSH) based on LSPR scattering spectrum using gold core-satellite nanostructure linked by T-Hg²⁺-T base pair. The core-satellite assembly caused coupling between plasmonic nanoparticles, which inducing distinct change of LSPR peak wavelength. As the interaction between Hg²⁺ and GSH, the core-satellite nanostructure would be disassembled, which accompanied with spectral blue-shift of the scattering spectrum. By using this method, GSH could be quantitatively detected, and the detection limits can reach to 0.1 µM.

Ferromagnetic Resonance Biosensor for Homogeneous and Volumetric Detection of DNA

The ability to detect and analyze the state of magnetic labels with high sensitivity is of crucial importance for developing magnetic biosensors. In this work, we demonstrate, for the first time, a ferromagnetic resonance (FMR) based homogeneous and volumetric biosensor for magnetic label detection. Two different isothermal amplification methods, i.e., rolling circle amplification (RCA) and loop-mediated isothermal amplification (LAMP), are adopted and combined with a standard electron paramagnetic resonance (EPR) spectrometer for FMR biosensing. For the RCA-based FMR biosensor, binding of RCA products of a synthetic Vibrio cholerae target DNA sequence gives rise to the formation of aggregates of magnetic nanoparticles. Immobilization of nanoparticles within the aggregates leads to a decrease of the net anisotropy of the system and a concomitant increase of the resonance field. A limit of detection of 1 pM is obtained with a linear detection range between 7.8 and 250 pM. For the LAMP-based sensing, a synthetic Zika virus target oligonucleotide is amplified and detected in 20% serum samples. Immobilization of magnetic nanoparticles is induced by their coprecipitation with Mg₂P₂O₇ (a byproduct of LAMP) and provides a detection sensitivity of 100 aM. The fast measurement, high sensitivity, and miniaturization potential of the proposed FMR biosensing technology makes it a promising candidate for designing future point-of-care devices.

Nanoplasmonic sensors for biointerfacial science

In recent years, nanoplasmonic sensors have become widely used for the label-free detection of biomolecules across medical, biotechnology, and environmental science applications. To date, many nanoplasmonic sensing strategies have been developed with outstanding measurement capabilities, enabling detection down to the single-molecule level. One of the most promising directions has been surface-based nanoplasmonic sensors, and the potential of such technologies is still emerging. Going beyond detection, surface-based nanoplasmonic sensors open the door to enhanced, quantitative measurement capabilities across the biointerfacial sciences by taking advantage of high surface sensitivity that pairs well with the size of medically important biomacromolecules and biological particulates such as viruses and exosomes. The goal of this review is to introduce the latest advances in nanoplasmonic sensors for the biointerfacial sciences, including ongoing development of nanoparticle and nanohole arrays for exploring different classes of biomacromolecules interacting at solid-liquid interfaces. The measurement principles for nanoplasmonic sensors based on utilizing the localized surface plasmon resonance (LSPR) and extraordinary optical transmission (EOT) phenomena are first introduced. The following sections are then categorized around different themes within the biointerfacial sciences, specifically protein binding and conformational changes, lipid membrane fabrication, membrane-protein interactions, exosome and virus detection and analysis, and probing nucleic acid conformations and binding interactions. Across these themes, we discuss the growing trend to utilize nanoplasmonic sensors for advanced measurement capabilities, including positional sensing, biomacromolecular conformation analysis, and real-time kinetic monitoring of complex biological interactions. Altogether, these advances highlight the rich potential of nanoplasmonic sensors and the future growth prospects of the community as a whole. With ongoing development of commercial nanoplasmonic sensors and analytical models to interpret corresponding measurement data in the context of biologically relevant interactions, there is significant opportunity to utilize nanoplasmonic sensing strategies for not only fundamental biointerfacial science, but also translational science applications related to clinical medicine and pharmaceutical drug development among countless possibilities.

Understanding and improving aggregated gold nanoparticle/dsDNA interactions by molecular spectroscopy and deconvolution methods

It is well known that single-stranded DNA (ssDNA) is easily able to adsorb on citrate-capped, non-functionalized gold nanoparticles (AuNPs). However, the affinity of double-stranded DNA (dsDNA) for them is much more limited. The present work demonstrates that long dsDNA suffers from a bending conformational change when anionic nanoparticles are present in solution. A striking decrease in the persistence length of the double helix in the absence of salt is observed through dynamic light scattering (DLS), viscometric, and atomic force microscopy (AFM) methods. Long dsDNA is therefore shown to be able to interact with anionic gold nanoparticles. To date, only ssDNA detection has been described by making use of interparticle cross-linking aggregation mechanisms; however, the data shown in this work allow for the development of new methods for detecting dsDNA in solution by using aggregated AuNPs as a starting point. The aggregation state is induced by the controlled addition of an inert electrolyte. A deconvolution procedure of the experimental plasmon shows how individual bands corresponding to aggregated nanoclusters diminish as the DNA concentration increases in the presence of 0.075 M NaCl.

A simple anti-solvent method for the controlled deposition of metal and alloy nanoparticles

Plasmonics of metal and alloy nanoparticles finds immense applications in materials science, medicine and advanced physics.

Gold nanoparticle-based colorimetric biosensors

Gold nanoparticles (AuNPs) provide excellent platforms for the development of colorimetric biosensors as they can be easily functionalised, displaying different colours depending on their size, shape and state of aggregation. In the last decade, a variety of biosensors have been developed to exploit the extent of colour changes as nano-particles (NPs) either aggregate or disperse, in the presence of analytes. Of critical importance to the design of these methods is that the behaviour of the systems has to be reproducible and predictable. Much has been accomplished in understanding the interactions between a variety of substrates and AuNPs, and how these interactions can be harnessed as colorimetric reporters in biosensors. However, despite these developments, only a few biosensors have been used in practice for the detection of analytes in biological samples. The transition from proof of concept to market biosensors requires extensive long-term reliability and shelf life testing, and modification of protocols and design features to make them safe and easy to use by the population at large. Developments in the next decade will see the adoption of user friendly biosensors for point-of-care and medical diagnosis as innovations are brought to improve the analytical performances and usability of the current designs. This review discusses the mechanisms, strategies, recent advances and perspectives for the use of AuNPs as colorimetric biosensors.

Tuning the Gold Nanoparticle Colorimetric Assay by Nanoparticle Size, Concentration, and Size Combinations for Oligonucleotide Detection

Gold nanoparticle (GNP)-based aggregation assay is simple, fast, and employs a colorimetric detection method. Although previous studies have reported using GNP-based colorimetric assay to detect biological and chemical targets, a mechanistic and quantitative understanding of the assay and effects of GNP parameters on the assay performance is lacking. In this work, we investigated this important aspect of the GNP aggregation assay including effects of GNP concentration and size on the assay performance to detect malarial DNA. Our findings lead us to propose three major competing factors that determine the final assay performance including the nanoparticle aggregation rate, plasmonic coupling strength, and background signal. First, increasing nanoparticle size reduces the Brownian motion and thus aggregation rate, but significantly increases plasmonic coupling strength. We found that larger GNP leads to stronger signal and improved limit of detection (LOD), suggesting a dominating effect of plasmonic coupling strength. Second, higher nanoparticle concentration increases the probability of nanoparticle interactions and thus aggregation rate, but also increases the background extinction signal. We observed that higher GNP concentration leads to stronger signal at high target concentrations due to higher aggregation rate. However, the fact the optimal LOD was found at intermediate GNP concentrations suggests a balance of two competing mechanisms between aggregation rate and signal/background ratio. In summary, our work provides new guidelines to design GNP aggregation-based POC devices to meet the signal and sensitivity needs for infectious disease diagnosis and other applications.

State of diagnosing infectious pathogens using colloidal nanomaterials

Infectious diseases are a major global threat that accounts for one of the leading causes of global mortality and morbidity. Prompt diagnosis is a crucial first step in the management of infectious threats, which aims to quarantine infected patients to avoid contacts with healthy individuals and deliver effective treatments prior to further spread of diseases. This review article discusses current advances of diagnostic systems using colloidal nanomaterials (e.g., gold nanoparticles, quantum dots, magnetic nanoparticles) for identifying and differentiating infectious pathogens. The challenges involved in the clinical translation of these emerging nanotechnology based diagnostic devices will also be discussed.

Enabling miniaturised personalised diagnostics: from lab-on-a-chip to lab-in-a-drop

The concept of personalised diagnostics is to direct accurate clinical decisions based on an individual's unique disease molecular profile. Lab-on-a-chip (LOC) systems are prime personalised diagnostics examples which seek to perform an entire sample-to-outcome detection of disease nucleic acid (NA) biomarkers on a single miniaturised platform with minimal user handling. Despite the great potential of LOC devices in providing rapid, portable, and inexpensive personalised diagnosis at the point-of-care (POC), the translation of this technology into widespread use has still been hampered by the need for sophisticated and complex engineering. As an alternative miniaturised diagnostics platform free of precision fabrication, there have been recent developments towards a solution-based lab-in-a-drop (LID) system by which an entire laboratory-based diagnostics workflow could be downscaled and integrated within a singular fluid droplet for POC detection of NA biomarkers. In contrast to existing excellent reviews on miniaturised LOC fabrication and individual steps of NA biomarker sensing, we herein focus on miniaturised solution-based NA biosensing strategies suited for integrated LID personalised diagnostics development. In this review, we first evaluate the three fundamental bioassay steps for miniaturised NA biomarker detection: crude sample preparation, isothermal target amplification, and detection readout of amplicons. Then, we provide insights into research advancements towards a functional LID system which integrates all three of the above-mentioned fundamental steps. Finally, we discuss perspectives and future directions of LID diagnostic platforms in personalised medicine applications.

High-Performance Colorimetric Detection of Thiosulfate by Using Silver Nanoparticles for Smartphone-Based Analysis

Developing thiosulfate (S₂O₃^2-) sensors with silver nanoparticles (AgNPs) for analysis of aqueous solutions with the interference of other anions remains challenging. In this study, we propose a new strategy for excellent selective colorimetric detection of S₂O₃^2-. The nonmorphological transition of AgNPs leading to a color change from yellow to brown is verified by UV-vis, TEM, DLS, SEM, and XPS analyses. The sensor exhibits high sensitivity with detection limits of 1.0 μM by naked-eye determination and 0.2 μM by UV-vis spectroscopy analysis. The linear relationship (R² = 0.998) between the (A₀ - A)/A₀ values and S₂O₃^2- concentrations from 0.2 μM to 2.0 μM indicates that the fabricated AgNPs-based colorimetric sensor can be employed for quantitative assay of S₂O₃^2-. Colorimetric responses are also monitored using the built-in camera of a smartphone. The sensor shows a linear response to S₂O₃^2- in 0-20.0 μM solutions under the optimized conditions and is thus more suitable for rapid on-site tests than other detection methods. A smartphone application (app) is downloaded under Android or IOS platforms to measure the RGB (red, green, blue) values of the colorimetric sensor after exposure to the analyte. Following data processing, the RGB values are converted into concentration values by using preloaded calibration curves. Confirmatory analysis indicates that the proposed S₂O₃^2- colorimetric sensor exhibits feasibility and sensitivity for S₂O₃^2- detection in real environmental samples.

Applicability of Metal Nanoparticles in the Detection and Monitoring of Hepatitis B Virus Infection

Chronic infection with the hepatitis B virus (HBV) can lead to liver failure and can cause liver cirrhosis and hepatocellular carcinoma (HCC). Reliable means for detecting and monitoring HBV infection are essential to identify patients in need of therapy and to prevent HBV transmission. Nanomaterials with defined electrical, optical, and mechanical properties have been developed to detect and quantify viral antigens. In this review, we discuss the challenges in applying nanoparticles to HBV antigen detection and in realizing the bio-analytical potential of such nanoparticles. We discuss recent developments in generating detection platforms based on gold and iron oxide nanoparticles. Such platforms increase biological material detection efficiency by the targeted capture and concentration of HBV antigens, but the unique properties of nanoparticles can also be exploited for direct, sensitive, and specific antigen detection. We discuss several studies that show that nanomaterial-based platforms enable ultrasensitive HBV antigen detection.

Nanotechnology-Enhanced No-Wash Biosensors for in Vitro Diagnostics of Cancer

In vitro biosensors have been an integral component for early diagnosis of cancer in the clinic. Among them, no-wash biosensors, which only depend on the simple mixing of the signal generating probes and the sample solution without additional washing and separation steps, have been found to be particularly attractive. The outstanding advantages of facile, convenient, and rapid response of no-wash biosensors are especially suitable for point-of-care testing (POCT). One fast-growing field of no-wash biosensor design involves the usage of nanomaterials as signal amplification carriers or direct signal generating elements. The analytical capacity of no-wash biosensors with respect to sensitivity or limit of detection, specificity, stability, and multiplexing detection capacity is largely improved because of their large surface area, excellent optical, electrical, catalytic, and magnetic properties. This review provides a comprehensive overview of various nanomaterial-enhanced no-wash biosensing technologies and focuses on the analysis of the underlying mechanism of these technologies applied for the early detection of cancer biomarkers ranging from small molecules to proteins, and even whole cancerous cells. Representative examples are selected to demonstrate the proof-of-concept with promising applications for in vitro diagnostics of cancer. Finally, a brief discussion of common unresolved issues and a perspective outlook on the field are provided.

Diverse Applications of Nanomedicine

The design and use of materials in the nanoscale size range for addressing medical and health-related issues continues to receive increasing interest. Research in nanomedicine spans a multitude of areas, including drug delivery, vaccine development, antibacterial, diagnosis and imaging tools, wearable devices, implants, high-throughput screening platforms, etc. using biological, nonbiological, biomimetic, or hybrid materials. Many of these developments are starting to be translated into viable clinical products. Here, we provide an overview of recent developments in nanomedicine and highlight the current challenges and upcoming opportunities for the field and translation to the clinic.