Colorimetric assay for protein detection based on "nano-pumpkin" induced aggregation of peptide-decorated gold nanoparticles

Electrochemiluminescence and electrochemical dual-mode detection of BACE1 activity based on the assembly of peptide and luminol co-functionalized silver nanoparticles induced by cucurbit[8]uril

A novel electrochemiluminescence (ECL) and electrochemical dual-mode sensor was developed for detecting the activity of beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) and screening its inhibitor. Specifically, the adamantane (ADA)-functionalized peptide (P1), a designed substrate peptide for BACE1, was immobilized on the electrode surface via host-guest interaction between β-cyclodextrin (β-CD) and ADA. The aggregation of the peptide (P2) and luminol co-functionalized silver nanoparticles could be induced by cucurbit [8]uril (CB[8] due to the ability of CB[8] to accommodate two aromatic residues simultaneously. The obtained (CB[8]-P2-AgNPs-luminol)n aggregates with both ECL and electrochemical activity, used as the dual-mode signal probe, could be captured to the N-terminal of P1 through CB[8]. Once the substrate P1 was cleaved by BACE1, the probe-binding polypeptide fragment detached from the electrode surface, resulting in a remarkable decrease in the ECL and electrochemical signals. Taking advantage of the signal amplification function of the signal probe, the sensitive dual-mode assay for BACE1 activity can be achieved with the low detection limits of 33.11 pM for ECL and 53.19 pM for electrochemical mode. The superior analytical performance of this novel dual-mode sensor toward BACE1 activity suggested the promising application in early diagnosis of Alzheimer's disease (AD).

Recent Advances in Design and Application of Nanomaterials-Based Colorimetric Biosensors for Agri-food Safety Analysis

A colorimetric sensor detects an analyte by utilizing the optical properties of the sensor unit, such as absorption or reflection, to generate a structural color that serves as the output signal to detect an analyte. Detecting the refractive index of an analyte by recording the color change of the sensor structure on its surface has several advantages, including simple operation, low cost, suitability for onsite analysis, and real-time detection. Colorimetric sensors have drawn much attention owing to their rapidity, simplicity, high sensitivity and selectivity. This Review discusses the use of colorimetric sensors in the food industry, including their applications for detecting food contaminants. The Review also provides insight into the scope of future research in this area.

Functionalization of in vivo tissue-engineered living biotubes enhance patency and endothelization without the requirement of systemic anticoagulant administration

Vascular regeneration and patency maintenance, without anticoagulant administration, represent key developmental trends to enhance small-diameter vascular grafts (SDVG) performance. In vivo engineered autologous biotubes have emerged as SDVG candidates with pro-regenerative properties. However, mechanical failure coupled with thrombus formation hinder translational prospects of biotubes as SDVGs. Previously fabricated poly(ε-caprolactone) skeleton-reinforced biotubes (PBs) circumvented mechanical issues and achieved vascular regeneration, but orally administered anticoagulants were required. Here, highly efficient and biocompatible functional modifications were introduced to living cells on PB lumens. The 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-N-methoxy (DMPE)-PEG-conjugated anti-coagulant bivalirudin (DPB) and DMPE-PEG-conjugated endothelial progenitor cell (EPC)-binding TPS-peptide (DPT) modifications possessed functionality conducive to promoting vascular graft patency. Co-modification of DPB and DPT swiftly attained luminal saturation without influencing cell viability. DPB repellent of non-specific proteins, DPB inhibition of thrombus formation, and DPB protection against functional masking of DPT's EPC-capture by blood components, which promoted patency and rapid endothelialization in rat and canine artery implantation models without anticoagulant administration. This strategy offers a safe, facile, and fast technical approach to convey additional functionalization to living cells within tissue-engineered constructs.

Site-directed dual bioprobes inducing single-step nano-sandwich assay for the detection of cardiac troponin I

Bioreceptor functionalized metallic nano-colloids have been identified as effective nanobioprobes to realize the detection of an analyte based on a common phenomenon of salt-induced aggregation. In marked contrast to this, we describe a nano-sandwich assay integrating the novel match-pair of aptamer and peptide functionalized gold nanoparticles. The site-directed biomolecular interaction of high affinity aptamer and peptide bioreceptors directed towards distinct sites of cardiac biomarker troponin I; this was found to form a nano-sandwich assay in a peculiar manner. The gold nanoconjugates interact with specific and distant regions of troponin I to result in collision of probes upon target identification. In the presence of TnI, both nanobioprobes bind at their respective sites forming a nano-sandwich pair providing a visual color change from red to blue. Thus, the presence of target TnI itself causes instant agglomeration in just a single-step without addition of any external aggregator. The assay imparts 100% specificity and 90% sensitivity in a dynamic concentration range of 0.1-500 ng/mL troponin I with detection limit as low as 0.084 ng/mL. The applicability of the assay has been validated in clinical samples of acute myocardial infarction patients thus establishing a promising point-of-care detection of TnI.

Applications of laboratory findings in the prevention, diagnosis, treatment, and monitoring of COVID-19

The worldwide pandemic of coronavirus disease 2019 (COVID-19) presents us with a serious public health crisis. To combat the virus and slow its spread, wider testing is essential. There is a need for more sensitive, specific, and convenient detection methods of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Advanced detection can greatly improve the ability and accuracy of the clinical diagnosis of COVID-19, which is conducive to the early suitable treatment and supports precise prophylaxis. In this article, we combine and present the latest laboratory diagnostic technologies and methods for SARS-CoV-2 to identify the technical characteristics, considerations, biosafety requirements, common problems with testing and interpretation of results, and coping strategies of commonly used testing methods. We highlight the gaps in current diagnostic capacity and propose potential solutions to provide cutting-edge technical support to achieve a more precise diagnosis, treatment, and prevention of COVID-19 and to overcome the difficulties with the normalization of epidemic prevention and control.

Nucleotide-decorated AuNPs as probes for nucleotide-binding proteins

Gold nanoparticles (AuNPs) decorated with biologically relevant molecules have variety of applications in optical sensing of bioanalytes. Coating AuNPs with small nucleotides produces particles with high stability in water, but functionality-compatible strategies are needed to uncover the full potential of this type of conjugates. Here, we demonstrate that lipoic acid-modified dinucleotides can be used to modify AuNPs surfaces in a controllable manner to produce conjugates that are stable in aqueous buffers and biological mixtures and capable of interacting with nucleotide-binding proteins. Using this strategy we obtained AuNPs decorated with 7-methylguanosine mRNA 5' cap analogs and showed that they bind cap-specific protein, eIF4E. AuNPs decorated with non-functional dinucleotides also interacted with eIF4E, albeit with lower affinity, suggesting that eIF4E binding to cap-decorated AuNPs is partially mediated by unspecific ionic interactions. This issue was overcome by applying lipoic-acid-Tris conjugate as a charge-neutral diluting molecule. Tris-Lipo-diluted cap-AuNPs conjugates interacted with eIF4E in fully specific manner, enabling design of functional tools. To demonstrate the potential of these conjugates in protein sensing, we designed a two-component eIF4E sensing system consisting of cap-AuNP and 4E-BP1-AuNP conjugates, wherein 4E-BP1 is a short peptide derived from 4E-BP protein that specifically binds eIF4E at a site different to that of the 5' cap. This system facilitated controlled aggregation, in which eIF4E plays the role of the agent that crosslinks two types of AuNP, thereby inducing a naked-eye visible absorbance redshift. The reported AuNPs-nucleotide conjugation method based on lipoic acid affinity for gold, can be harnessed to obtain other types of nucleotide-functionalized AuNPs, thereby paving the way to studying other nucleotide-binding proteins.

The Peptide Functionalized Inorganic Nanoparticles for Cancer-Related Bioanalytical and Biomedical Applications

In order to improve their bioapplications, inorganic nanoparticles (NPs) are usually functionalized with specific biomolecules. Peptides with short amino acid sequences have attracted great attention in the NP functionalization since they are easy to be synthesized on a large scale by the automatic synthesizer and can integrate various functionalities including specific biorecognition and therapeutic function into one sequence. Conjugation of peptides with NPs can generate novel theranostic/drug delivery nanosystems with active tumor targeting ability and efficient nanosensing platforms for sensitive detection of various analytes, such as heavy metallic ions and biomarkers. Massive studies demonstrate that applications of the peptide-NP bioconjugates can help to achieve the precise diagnosis and therapy of diseases. In particular, the peptide-NP bioconjugates show tremendous potential for development of effective anti-tumor nanomedicines. This review provides an overview of the effects of properties of peptide functionalized NPs on precise diagnostics and therapy of cancers through summarizing the recent publications on the applications of peptide-NP bioconjugates for biomarkers (antigens and enzymes) and carcinogens (e.g., heavy metallic ions) detection, drug delivery, and imaging-guided therapy. The current challenges and future prospects of the subject are also discussed.

Specific intracellular binding peptide as sPD-L1 antibody mimic: Robust binding capacity and intracellular region specific modulation upon applied to sensing research

Programmed death ligand 1 (PD-L1) immune checkpoint has been regarded as a new target for predicting cancer immunotherapy. As a transmembrane protein, PD-L1 has very low blood concentration and is likely to deplete their native activity when separated from the membrane environment due to significant hydrophobic domains, which make it difficult to measure sensitively. The reported PD-L1 aptamers and antibodies are both extracellular region binding molecules with the overlapping binding sites, which seriously limit with the construction of biosensor. Specific intracellular binding peptide (SIBP) as a unique PD-L1 intracellular region homing probe molecule is utilized for specifically capture targets. A simple and sensitive surface plasmon resonance (SPR) sandwich assay was constructed to detect serum soluble PD-L1 (sPD-L1) based on the unique and strong binding ability of SIBP to the intracellular region of sPD-L1. The designed SPR sensor showed great selectivity and wide dynamic response range of sPD-L1 concentration from 10 ng/mL to 2000 ng/mL. The limit of detection was calculated to be 1.749 ng/mL (S/N = 3). Owing to the SIBP's strong and specific binding ability with sPD-L1, the sensitive sensor can successfully detect sPD-L1 in serum samples, paving the way for the development of efficient test tools for clinical diagnosis and analysis.

Recent Advancements in Nanoparticle-Based Optical Biosensors for Circulating Cancer Biomarkers

The effectiveness of cancer treatment strongly depends on the early detection of the disease. Currently, the most common diagnostic method, tissue biopsy, takes time and can be damaging to the patient. Circulating cancer biomarkers such as circulating tumor DNA, micro-RNA (miRNA), tumor proteins, exosomes, and circulating tumor cells have repeatedly demonstrated their viability as targets for minimally invasive cancer detection through liquid biopsies. However, among other things, achieving a great sensitivity of detection is still challenging due to the very low concentration of biomarkers in fluid samples. This review will discuss how the recent advances in nanoparticle-based biosensors are overcoming these practical difficulties. This report will be focusing mainly on optical transduction mechanisms of metal nanoparticles (M-NPs), quantum dots (QDs), and upconversion nanoparticles (UCNPs).

Chemical sensing with Au and Ag nanoparticles

Noble metal nanoparticles (NPs) are ideal scaffolds for the fabrication of sensing devices because of their high surface-to-volume ratio combined with their unique optical and electrical properties which are extremely sensitive to changes in the environment. Such characteristics guarantee high sensitivity in sensing processes. Metal NPs can be decorated with ad hoc molecular building blocks which can act as receptors of specific analytes. By pursuing this strategy, and by taking full advantage of the specificity of supramolecular recognition events, highly selective sensing devices can be fabricated. Besides, noble metal NPs can also be a pivotal element for the fabrication of chemical nose/tongue sensors to target complex mixtures of analytes. This review highlights the most enlightening strategies developed during the last decade, towards the fabrication of chemical sensors with either optical or electrical readout combining high sensitivity and selectivity, along with fast response and full reversibility, with special attention to approaches that enable efficient environmental and health monitoring.

Functionalized gold nanoparticles: promising and efficient diagnostic and therapeutic tools for HIV/AIDS

Functionalized gold nanoparticles are recognized as promising vehicles in the diagnosis and treatment of human immunodeficiency virus (HIV) owing to their excellent biocompatibility with biomolecules (like DNA or RNA), their potential for multivalency and their unique optical and structural properties. In this context, this review article focuses on the diverse detection abilities and delivery and uptake methodologies of HIV by targeting genes and proteins using gold nanoparticles on the basis of different shapes and sizes in order to promote its effective expression. In addition, recent trends in gold nanoparticle mediated HIV detection, delivery and uptake and treatment are highlighted considering their cytotoxic effects on healthy human cells.

An electrogenerated chemiluminescence aptasensor for lysozyme based on the interaction between Ru(bpy)3 2+ and cucurbit[8]uril

Strong anodic Ru(bpy)₃ ²⁺ electrogenerated chemiluminescence (ECL) was obtained at a cucurbil[8]uril (CB[8]) modified electrode in neutral conditions without the need of an additional coreactant. An ECL aptasensor was fabricated based on the strong ECL emission as well as the host-guest interaction between DNA and CB[8]. Firstly, amino group-terminated complementary DNA (DNA-NH₂ ) was firmly immobilized on CB[8]/glass carbon electrode, which could further increase ECL intensity. Then, a ferrocene group-terminated lysozyme aptamer (Fc-DNA) was hybridized with complementary DNA. The inhibiting effect of ferrocene on Ru(bpy)₃ ²⁺ ECL resulted in the apparent decrease in ECL signal. When the modified electrode was incubated in lysozyme, specific binding between lysozyme and its aptamer could release the ferrocene group from the electrode surface, and the ECL emission was recovered. As a result, an 'on-off-on' mode ECL aptasensor for lysozyme was fabricated. In the range 0.14-140 pg ml^-1 , the increased ECL intensities exhibited excellent linearity with the logarithm of lysozyme concentrations, and the detection limit was calculated as 0.093 pg ml^-1 (3σ). The proposed ECL aptasensor exhibited satisfactory analytical performance, revealing the potential application of CB[n]s in an ECL sensing field.

Rational Design of Functional Peptide-Gold Hybrid Nanomaterials for Molecular Interactions

Gold nanoparticles (AuNPs) have been extensively used for decades in biosensing-related development due to outstanding optical properties. Peptides, as newly realized functional biomolecules, are promising candidates of replacing antibodies, receptors, and substrates for specific molecular interactions. Both peptides and AuNPs are robust and easily synthesized at relatively low cost. Hence, peptide-AuNP-based bio-nano-technological approaches have drawn increasing interest, especially in the field of molecular targeting, cell imaging, drug delivery, and therapy. Many excellent works in these areas have been reported: demonstrating novel ideas, exploring new targets, and facilitating advanced diagnostic and therapeutic technologies. Importantly, some of them also have been employed to address real practical problems, especially in remote and less privileged areas. This contribution focuses on the application of peptide-gold hybrid nanomaterials for various molecular interactions, especially in biosensing/diagnostics and cell targeting/imaging, as well as for the development of highly active antimicrobial/antifouling coating strategies. Rationally designed peptide-gold nanomaterials with functional properties are discussed along with future challenges and opportunities.

Targeted Repair of Vascular Injury by Adipose-Derived Stem Cells Modified with P-Selectin Binding Peptide

Percutaneous coronary intervention for coronary artery disease treatment often results in pathological vascular injury, characterized by P-selectin overexpression. Adipose-derived stem cells (ADSCs) therapeutic efficacy remains elusive due to poor ADSCs targeting and retention in injured vessels. Here, conjugated P-selectin binding peptide (PBP) to polyethylene glycol-conjugated phospholipid derivative (DMPE-PEG) linkers (DMPE-PEG-PBP; DPP) are used to facilitate the modification of PBP onto ADSCs cell surfaces via hydrophobic interactions between DMPE-PEG and the phospholipid bilayer. DPP modification neither has influence on ADSCs proliferation nor apoptosis/paracrine factor gene expression. A total of 5 × 10^-6 m DPP-modified ADSCs (DPP-ADSCs) strongly binds to P-selectin-displaying activated platelets and endothelial cells (ECs) in vitro and to wire-injured rat femoral arteries when administered by intra-arterial injection. Targeted binding of ADSCs shields injury sites from platelet and leukocyte adhesion, thereby decreasing inflammation at injury sites. Furthermore, targeted binding of ADSCs recovers injured ECs functionality and reduces platelet-initiated vascular smooth muscle cells (VSMCs) chemotactic migration. Targeted binding of DPP-human ADSCs to balloon-injured human femoral arteries is also demonstrated in ex vivo experiments. Overall, DPP-ADSCs promote vascular repair, inhibit neointimal hyperplasia, increase endothelium functionality, and maintain normal VSMCs alignment, supporting preclinical noninvasive utilization of DPP-ADSCs for vascular injury.

A rapid and ultrasensitive colorimetric biosensor based on aptamer functionalized Au nanoparticles for detection of saxitoxin

We demonstrate a facile and ultrasensitive colorimetric sensor based on gold nanoparticles (Au NPs) and aptamer (Au NPs-aptamer biosensor) for specific and quantitative detection of STX.

Visual and spectrophotometric detection of metformin based on the host-guest molecular recognition of cucurbit[6]uril-modified silver nanoparticles

A simple, sensitive, and naked-eye assay of metformin (MET), based on the host-guest molecular recognition of cucurbit[6]uril (CB[6])-modified silver nanoparticles, has been developed for the first time. The molecular recognition between CB[6] and MET is initially demonstrated and the related recognition mechanism is further discussed. CB[6]-modified AgNPs were first synthesized and then characterized by UV-vis spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy. The solution behavior of CB[6] in the presence of AgNO₃ was also studied, and the correlative result revealed that AgNPs could combine with the carbonyl portals of CB[6]. On the basis of the molecular recognition of CB[6] and the surface plasmon resonance effect of AgNPs, CB[6]-modified AgNPs were used as visual probes to detect MET. In CB[6]-modified AgNP solution, the aggregation of CB[6]-modified AgNPs induced by MET triggered changes of color and the UV-vis absorption spectrum, which laid the foundation for the visual identification and spectrophotometric determination of MET. Under the optimized detection conditions, the UV-vis spectral assay had a good linear relationship in the range from 3 to 750 μM, and the limit of detection was 1 μM. According to the color changes, the minimum concentration recognized by the naked eye was about 75 μM. Furthermore, this assay has high selectivity for coexisting interferents and was also applied to MET detection in human urine samples. This strategy provides a novel and facile tool for highly selective and sensitive detection of MET. Graphical abstract.

Colorimetric detection of Ba2+, Cd2+ and Pb2+ based on a multifunctionalized Au NP sensor

A colorimetric method for the detection of three kinds of ions in water with one kind of detection reagent was developed.

Supramolecularly Multicolor DNA Decoding Using an Indicator Competition Assay

Relative to the individual intensity-dependent strategy, the multicolor fluorescence sensor has promise to achieve a high signaling contrast. In this work, we develop a cucurbituril-based supramolecular and multicolor DNA recognition rationale via indicator competition assay (ICA). Alkaloids of coptisine (COP) and palmatine (PAL) are identified as the proof-of-principle indicators with a lighting-up fluorescence upon supramolecular complexation to cucurbit[7]uril (CB[7]). With an introduced abasic site (AP site) as the contestant, DNAs having pyrimidines opposite this site can compete for COP with CB[7] to bring an emission color change from green to yellow brown, while those having purines opposite the AP site do not compete for COP and still have the green emission, indicative of a high selectivity for the multicolor nucleotide transversion recognition. However, because of the relatively weaker binding of PAL with CB[7], the AP site-containing DNA can take away PAL from its CB[7] complex and resultantly bring a blue-to-green emission color change independent of the AP site-opposite nucleotide identity, dissimilar to the remaining blue color for the fully matched DNA without the AP site, suggesting a preferable strategy for the AP site biomarker detection. Our method demonstrates a new way to develop an ICA-based multicolor DNA sensor with the supramolecular cucurbituril complexation to ensure a highly selective performance.

Optical assays based on colloidal inorganic nanoparticles

Colloidal inorganic nanoparticles have wide applications in the detection of analytes and in biological assays. A large number of these assays rely on the ability of gold nanoparticles (AuNPs, in the 20 nm diameter size range) to undergo a color change from red to blue upon aggregation. AuNP assays can be based on cross-linking, non-cross linking or unmodified charge-based aggregation. Nucleic acid-based probes, monoclonal antibodies, and molecular-affinity agents can be attached by covalent or non-covalent means. Surface plasmon resonance and SERS techniques can be utilized. Silver NPs also have attractive optical properties (higher extinction coefficient). Combinations of AuNPs and AgNPs in nanocomposites can have additional advantages. Magnetic NPs and ZnO, TiO2 and ZnS as well as insulator NPs including SiO2 can be employed in colorimetric assays, and some can act as peroxidase mimics in catalytic applications. This review covers the synthesis and stabilization of inorganic NPs and their diverse applications in colorimetric and optical assays for analytes related to environmental contamination (metal ions and pesticides), and for early diagnosis and monitoring of diseases, using medically important biomarkers.

Fabrication of reusable electrochemical biosensor and its application for the assay of α-glucosidase activity

A reusable biosensor has been fabricated in this work for the assay of α-glucosidase activity and the inhibitor screening. In this design, the aptamer of ATP is split as split aptamer 1 (Apt 1) and split aptamer 2 (Apt 2), and Apt 2 can link gold nanoparticles (AuNPs) modified with Apt 1 and 4-aminophenyl-α-d-glucopyranoside (pAPG). Consequently, the functional AuNPs can be immobilized onto the surface of gold electrode, allowing for salt-induced regeneration. In the presence of α-glucosidase, the glycosyl of pAPG is cut off, and the electroactive phenolic hydroxyls appear to give a strong current signal. Furthermore, the biosensor can be recovered very easily by incubating it in water to dissociate the AuNPs modified with Apt 1 and pAPG. So, a new biosensor for α-glucosidase activity detection and inhibitor screening is developed based on enzyme-activated signal generation and recovery. The biosensor may also exhibit good sensitivity for α-glucosidase determination with the detection limit 0.005 U/mL and can be reused by water-washing regeneration with good repeatability. Meanwhile this biosensor can also be utilized for inhibitor screening, which may have potential for clinical applications.

Optical and Electrochemical Aptasensors for Sensitive Detection of Streptomycin in Blood Serum and Milk

Detection and quantitation of antibiotic residues in blood serum and foodstuffs are in great demand. We have developed aptasensors for detection of streptomycin using electrochemical and optical methods. In the first method, an electrochemical aptasensor was developed for sensitive and selective detection of streptomycin, based on combination of exonuclease I (Exo I), complementary strand of aptamer (CS), arch shaped structure of aptamer (Apt)-CS conjugate, and gold electrode. The designed electrochemical aptasensor exhibited high selectivity toward streptomycin with a limit of detection (LOD) as low as 11.4 nM. Moreover, the developed electrochemical aptasensor was successfully used to detect streptomycin in milk and serum with LODs of 14.1 and 15.3 nM, respectively. In the second method, fluorescence quenching and colorimetric aptasensors were designed for detection of streptomycin based on aqueous gold nanoparticles (AuNPs) and double-stranded DNA (dsDNA). In the absence of streptomycin, aptamer/FAM-labeled complementary strand dsDNA is stable, resulting in the aggregation of AuNPs by salt bridge and an obvious color change from red to blue and strong emission of fluorescence. The colorimetric and fluorescence quenching aptasensors showed excellent selectivity toward streptomycin with limit of detections as low as 73.1 and 47.6 nM, respectively. The presented aptasensors were successfully used to detect streptomycin in milk and serum. For serum, LODs were determined to be 58.2 and 102.4 nM for fluorescence quenching and colorimetric aptasensors, respectively. For milk, LODs were calculated to be 56.2 and 108.7 nM for fluorescence quenching and colorimetric aptasensors, respectively.

Plasmon-Based Colorimetric Nanosensors for Ultrasensitive Molecular Diagnostics

Colorimetric detection of target analytes with high specificity and sensitivity is of fundamental importance to clinical and personalized point-of-care diagnostics. Because of their extraordinary optical properties, plasmonic nanomaterials have been introduced into colorimetric sensing systems, which provide significantly improved sensitivity in various biosensing applications. Here we review the recent progress on these plasmonic nanoparticles-based colorimetric nanosensors for ultrasensitive molecular diagnostics. According to their different colorimetric signal generation mechanisms, these plasmonic nanosensors are classified into two categories: (1) interparticle distance-dependent colorimetric assay based on target-induced forming cross-linking assembly/aggregate of plasmonic nanoparticles; and (2) size/morphology-dependent colorimetric assay by target-controlled growth/etching of the plasmonic nanoparticles. The sensing fundamentals and cutting-edge applications will be provided for each of them, particularly focusing on signal generation and/or amplification mechanisms that realize ultrasensitive molecular detection. Finally, we also discuss the challenge and give our future perspective in this emerging field.

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.

Application of aptamers in treatment and diagnosis of leukemia

Leukemia is a cancer of blood cells and bone marrow, leading to death in many patients mainly in children. Over the last several years, aptamers generated by SELEX (Systematic evolution of ligands by exponential enrichment) method, have quickly become a new class of targeting ligands for drug delivery applications and recently have been widely exploited in different biomedical applications, due to several potent properties such as high binding affinity and selectivity, low or no immunogenicity and toxicity, low cost and thermal stability. In this review, we presented in details about aptamers involved in targeting, and treatment of leukemia. Moreover, some analytical approaches such as electrochemical and optical aptasensors were introduced for detection and diagnosis of leukemia. Finally, we discussed about the directions and challenges of aptamer application in this field.

Biopolymer/gold nanoparticles composite plasmonic thermal history indicator to monitor quality and safety of perishable bioproducts

Quality and safety of perishable products such as foods, pharmaceutics, and biologicals is a constant concern. We have developed a plasmonic thermal history indicator (THI) taking advantage of the localized surface plasmon resonance of gold nanoparticles (AuNPs) synthesized in situ in alginate, a natural polysaccharide. The color of the THIs becomes more intense with increased storage temperature and/or duration, with the color changing from grey to red with time of exposure at high temperature (40°C). The results suggest that decreasing viscosity with increasing number of AuNPs being synthesized in the system, along with aggregation of newly synthesized AuNPs onto larger ones and their settling are potentially responsible for the distinct color change observed. The use of alginate in the THIs also facilitates fabricating them as solid hydrogel matrices by adding divalent calcium ions. This alginate-AuNPs THI system is tunable by altering its composition to suit different time-temperature monitoring scenarios and the color-change reaction is irreversible. The THI provides a convenient, reliable, safe, and inexpensive means for tracking the thermal history of perishable products without the need for a read-out device.

Supramolecular Chemistry-Assisted Electrochemical Method for the Assay of Endogenous Peptidylarginine Deiminases Activities

Peptidylarginine deiminase 4 (PAD4) is the only isoform of PADs located within the cell nucleus, which has been known to be related to several human diseases. In this work, we have proposed an electrochemical method for the assay of endogenous PAD4 activities as well as the studies of PAD4 inhibitors by making use of the supramolecular chemistry-assisted signal labeling. Specifically, peptide probes P1 and P2, which separately contain cysteine residues and tripeptides FGG (Phe-Gly-Gly), can be self-assembled onto the surface of the gold electrode and silver nanoparticles, respectively. In the meantime, the peptide probes can be connected together through cucurbit[8]uril-mediated host-guest interaction. Nevertheless, after trypsin-catalyzed digestion, FGG at the N-terminal of P1 will be removed from the electrode surface, thereby inhibiting the connection of P1 and P2. Since PAD4 catalyzes the citrullination of arginine residue within P1, trypsin-catalyzed digestion of P1 can be prohibited by the addition of PAD4. Consequently, an obvious change of the electrochemical response can be obtained from the silver nanoparticles (AgNPs) immobilized on the electrode surface. Experimental results have shown that our method can display an improved sensitivity and specificity for both PAD4 assay and inhibitor screening, which may effectively trace endogenous PAD4 and the inhibitors in the cancer cells. Therefore, our method may have great potential for the diagnosis and treatment of PAD4-related diseases in the future.

Proximity ligation-induced assembly of DNAzymes for simple and cost-effective colourimetric detection of proteins with high sensitivity

A novel colourimetric method for protein assays is proposed based on proximity ligation induced assembly of Mg(2+)-dependent DNAzymes, which may offer simple, cost-effective, sensitive and selective detection of the target protein.

Sensitive and low-background electrochemical assay of corin activity via supramolecular recognition and rolling circle amplification

Corin is an important member of type II transmembrane serine proteases that is involved in a variety of cardiovascular and pregnancy-related diseases. Herein, a sensitive and low-background electrochemical method is proposed to assay the activity of corin. In principle, a peptide comprising both the substrate motif of corin and binding site of cucurbit[8]uril (CB[8]) is first designed and immobilized on the electrode surface. Thereafter, via CB[8]-mediated supramolecular recognition, a DNA-primer is recruited, subsequently triggering the rolling circle amplification (RCA) reaction. In this way, a succeeding propagation of DNA strands is achieved on the electrode surface, which would produce remarkable repelling effect against the electrochemical species [Fe(CN)6](3-/4-), and thereby yield a highly minimized background signal. However, in the presence of activated corin, the peptide is specifically recognized and cleaved, breaching the recruitment of DNA primer as well as the RCA reaction, which decreases the repulsion to [Fe(CN)6](3-/4-), leading to a remarkable electrochemical response. As a result, the proposed assay method can sensitively determine the activity of corin with a detection limit of 0.92 pM, and can further be directly used in maternal plasma samples. Therefore, this method may provide a promising tool for pathological research and clinical diagnosis of corin-related diseases.

A novel fluorescent aptasensor based on gold and silica nanoparticles for the ultrasensitive detection of ochratoxin A

Analytical approaches for the detection and quantitation of ochratoxin A (OTA) in blood serum and food products are high in demand. In this study, a fluorescent aptamer-based sensor (aptasensor) is developed for the selective and sensitive detection of OTA, based on a complementary strand of aptamer (CS) and two types of nanoparticles, gold nanoparticles (AuNPs) and silica nanoparticles (SNPs) coated with streptavidin. The fabricated aptasensor inherits the characteristics of SNPs, as enhancers of fluorescence intensity; AuNPs, such as large surface area and unique optical properties; and high affinity of the aptamer toward its target compared to its CS. In the absence of OTA, no FAM and biotin-labeled CS is in the environment of the SNPs coated with streptavidin, which leads to no fluorescence emission. In the presence of the target, an FAM and biotin-labeled CS-SNPs coated with streptavidin conjugate is formed, thus resulting in a very strong fluorescence emission. The designed fluorescent aptasensor exhibits high selectivity toward OTA with a limit of detection (LOD) as low as 0.098 nM. Furthermore, the fabricated aptasensor was successfully applied for the detection of OTA in grape juice and serum with LODs of 0.113 and 0.152 nM, respectively.

A novel fluorescent aptasensor based on hairpin structure of complementary strand of aptamer and nanoparticles as a signal amplification approach for ultrasensitive detection of cocaine

Cocaine is one of the most commonly misused stimulant which could influence the central nervous system. In this study, a fluorescent aptamer-based sensor (aptasensor) was designed for sensitive and selective detection of cocaine, based on hairpin structure of complementary strand of aptamer (CS), target-induced release of aptamer (Apt) from CS and two kinds of nanoparticles, including silica nanoparticles (SNPs) coated with streptavidin and gold nanoparticles (AuNPs). The designed aptasensor acquires characteristics of AuNPs such as unique optical properties and large surface area, SNPs as amplifiers of fluorescence intensity, higher affinity of Apt toward its target relative to its CS, and finally the hairpin structure of CS that brings the fluorophore (FAM) to close proximity to the surface of SNPs. In the absence of cocaine, FAM is in close proximity to the surface of AuNPs, resulting in a weak fluorescence emission. In the presence of target, FAM comes to close proximity to the surface of SNPs because of the formation of hairpin structure of CS, leading to a very strong fluorescence emission. The fabricated fluorescent aptasensor exhibited a good selectivity toward cocaine with a limit of detection (LOD) as low as 209 pM. Moreover, the designed aptasensor was successfully utilized to detect cocaine in serum with a LOD as low as 293 pM.

A novel colorimetric sandwich aptasensor based on an indirect competitive enzyme-free method for ultrasensitive detection of chloramphenicol

Analytical methods for detection and quantitation of chloramphenicol in blood serum and foodstuffs arse highly in demand. In this study, a colorimetric sandwich aptamer-based sensor (aptasensor) was fabricated for sensitive and selective detection of chloramphenicol, based on an indirect competitive enzyme-free assay using gold nanoparticles (AuNPs), biotin and streptavidin. The designed aptasensor acquires characteristics of AuNPs, including large surface area and unique optical properties, and strong interaction of biotin with streptavidin. In the absence of chloramphenicol, the sandwich structure of aptasensor forms, leading to the observation of sharp red color. In the presence of target, functionalized AuNPs could not bind to 96-well plates, resulting in a faint red color. The fabricated colorimetric aptasensor exhibited high selectivity toward chloramphenicol with a limit of detection as low as 451 pM. Moreover, the developed colorimetric aptasensor was successfully used to detect chloramphenicol in milk and serum with LODs of 697 and 601 pM, respectively.