Biosensing strategies based on organic-scaffolded metal nanoclusters for ultrasensitive detection of tumor markers

Pt/Zn-TCPP Nanozyme-Based Flexible Immunoassay for Dual-Mode Pressure-Temperature Monitoring of Low-Abundance Proteins

Pressure and temperature, as common physical parameters, are important for monitoring human health. In contrast, single-mode monitoring is prone to causing experimental errors. Herein, we innovatively designed a dual-mode flexible sensing platform based on a platinum/zinc-meso-tetrakis(4-carboxyphenyl)porphyrin (Pt/Zn-TCPP) nanozyme for the quantitative monitoring of carcinoembryonic antigen (CEA) in biological fluids with pressure and temperature readouts. The Pt/Zn-TCPP nanozyme with catalytic and photothermal efficiencies was synthesized by means of integrating photosensitizers into porous materials. The flexible sensing system after the antigen-antibody reaction recognized the pressure using a flexible skin-like pressure sensor with a digital multimeter readout, whereas the temperature was acquired via the photoheat conversion system of the Pt/Zn-TCPP nanozyme under 808 nm near-infrared (NIR) irradiation using a portable NIR imaging camera on a smartphone. Meanwhile, the dual-mode flexible sensing system was carried out on a homemade three-dimensional (3D)-printed device. Results revealed that the developed dual-mode immunosensing platform could exhibit good pressure and temperature responses within the dynamic range of 0.5-100 ng mL-1 CEA with the detection limits of 0.24 and 0.13 ng mL-1, respectively. In addition, the pressure and temperature were sensed simultaneously without crosstalk interference. Importantly, the dual-mode flexible immunosensing system can effectively avoid false alarms during the measurement, thus providing great potential for simple and low-cost development for point-of-care testing.

Optical nanosensors based on noble metal nanoclusters for detecting food contaminants: A review

Food contaminants present a significant threat to public health. In response to escalating global concerns regarding food safety, there is a growing demand for straightforward, rapid, and sensitive detection technologies. Noble metal nanoclusters (NMNCs) have garnered considerable attention due to their superior attributes compared to other optical materials. These attributes include high catalytic activity, excellent biocompatibility, and outstanding photoluminescence properties. These features render NMNCs promising candidates for crafting nanosensors for food contaminant detection, offering the potential for the development of uncomplicated, swift, sensitive, user-friendly, and cost-effective detection approaches. This review investigates optical nanosensors based on NMNCs, including the synthesis methodologies of NMNCs, sensing strategies, and their applications in detecting food contaminants. Furthermore, it involves a comparative assessment of the applications of NMNCs in optical sensing and their performance. Ultimately, this paper imparts fresh perspectives on the forthcoming challenges. Hitherto, optical (particularly fluorescent) nanosensors founded on NMNCs have demonstrated exceptional sensing capabilities in the realm of food contaminant detection. To enhance sensing performance, future research should prioritize atomically precise NMNCs synthesis, augmentation of catalytic activity and optical properties, development of high-throughput and multimode sensing, integration of NMNCs with microfluidic devices, and the optimization of NMNCs storage, shelf life, and transportation conditions.

Recent advances in the biomolecules mediated synthesis of nanoclusters for food safety analysis

The development of nanoclusters based on incorporating biomolecules like proteins, lipids, enzymes, DNA, surfactants, and chemical stabilizers creates a stable and high fluorescence bio-sensors promising future due to their high sensitivity, high level of detection and better selectivity. This review addresses a comprehensive and systematic overview of the recent development in synthesizing metal nanocluster by various strategized synthesis techniques. Significantly, the application of nanometal clusters for the detection of various food contaminants such as microorganisms, antibodies, drugs, pesticides, metal contaminants, amino acids, and other food flavors have been discussed briefly concerning the detection techniques, sensitivity, selectivity, and lower limit of detection. The review further gives a brief account on the future prospects in the synthesis of novel metal nanocluster-based biosensors, and their advantages, shortcomings, and potential perspectives toward their application in the field of food safety analysis.

A reagentless electrochemical immunosensor for sensitive detection of carcinoembryonic antigen based on the interface with redox probe-modified electron transfer wires and effectively immobilized antibody

Convenient and sensitive detection of tumors marked in serum samples is of great significance for the early diagnosis of cancers. Facile fabrication of reagentless electrochemical immunosensor with efficient sensing interface and high sensitivity is still a challenge. Herein, an electrochemical immunosensor was easily fabricated based on the easy fabrication of immunoassay interface with electron transfer wires, confined redox probes, and conveniently immobilized antibodies, which can achieve sensitive and reagentless determination of the tumor marker, carcinoembryonic antigen (CEA). Carboxyl multi-walled carbon nanotubes (MWCNTs) were firstly modified with an electrochemical redox probe, methylene blue (MB), which has redox potentials distinguished from those of redox molecules commonly existing in biological samples (for example, ascorbic acid and uric acid). After the as-prepared MB-modified MWCNT (MWCNT-MB) was coated on the supporting glassy carbon electrode (GCE), the MWCNT-MB/GCE exhibited improved active area and electron transfer property. Polydopamine (PDA) was then in situ synthesized through simple self-polymerization of dopamine, which acts as the bio-linker to covalently immobilize the anti-CEA antibody (Ab). The developed immunosensor could be applied for electrochemical detection of CEA based on the decrease in the redox signal of MB after specific binding of CEA and immobilized Ab. The fabricated immunosensor can achieve sensitive determination of CEA ranging from 10 pg/ml to 100 ng/ml with a limit of detection (LOD) of 0.6 pg/ml. Determination of CEA in human serum samples was also realized with high accuracy.

Bridging the Gap between Digital Assays and Point-of-Care Testing: Automated, Low Cost, and Ultrasensitive Detection of Thyroid Stimulating Hormone

Medical diagnostics is moving toward disease-related target detection at very low concentrations because of the (1) quest for early-stage diagnosis, at a point where only limited target amounts are present, (2) trend toward minimally invasive sample extraction, yielding samples containing low concentrations of target, and (3) need for straightforward sample collection, usually resulting in limited volume collected. Hence, diagnostic tools allowing ultrasensitive target detection at the point-of-care (POC) are crucial for simplified and timely diagnosis of many illnesses. Therefore, we developed an innovative, fully integrated, semi-automated, and economically viable platform based on (1) digital microfluidics (DMF), enabling automated manipulation and analysis of very low sample volumes and (2) low-cost disposable DMF chips with microwell arrays, fabricated via roll-to-roll processes and allowing digital target counting. Thyroid stimulating hormone detection was chosen as a relevant application to show the potential of the system. The assay buffer was selected using design of experiments, and the assay was optimized in terms of reagent concentration and incubation time toward maximum sensitivity. The hydrophobic-in-hydrophobic microwells showed an unparalleled seeding efficiency of 97.6% ± 0.6%. A calculated LOD of 0.0013 μIU/mL was obtained, showing the great potential of the platform, especially taking into account the very low sample volume analyzed (1.1 μL). Although validation (in biological matrix) and industrialization (full automation) steps still need to be taken, it is clear that the combination of DMF, low-cost DMF chips, and digital analyte counting in microwell arrays enables the implementation of ultrasensitive and reliable target detection at the POC.

An Eco-Friendly Synthetic Approach for Copper Nanoclusters and Their Potential in Lead Ions Sensing and Biological Applications

A new preparation route for high-luminescent blue-emission pepsin copper nanoclusters (Pep-CuNCs) is introduced in this work. The synthesized nanoclusters are based on a pepsin molecule, which is a stomach enzyme that works to digest proteins that exist in undigested food. Here, we have developed an eco-friendly technique through microwave-assisted fast synthesis. The resulting copper nanoclusters (CuNCs) exhibit significant selectivity towards Pb(II) ions. The pepsin molecule was utilized as a stabilizer and reducing agent in the production procedure of Pep-CuNCs. The characteristics of the resulting Pep-CuNCs were studied in terms of size, surface modification, and composition using various sophisticated techniques. The CuNCs responded to Pb(II) ions through the fluorescence quenching mechanism of the CuNCs' fluorescence. Thus, great selectivity of Pep-CuNCs towards Pb(II) ions was observed, allowing sensitive determination of this metal ion at lab-scale and in the environment. The CuNCs have detection limits for Pb(II) in very tenuous concentration at a nanomalar scale (11.54 nM). The resulting Pep-CuNCs were utilized significantly to detect Pb(II) ions in environmental samples. Additionally, the activity of Pep-CuNCs on different human tumor cell lines was investigated. The data for the observed behavior indicate that the Pep-CuNCs displayed their activity against cancer cells in a dose dependent manner against most utilized cancer cell lines.

Studies of probe tip materials by atomic force microscopy: a review

As a tool that can test insulators' surface morphology and properties, the performance index of atomic force microscope (AFM) probes is the most critical factor in determining the resolution of microscopy, and the performance of probes varies in various modes and application requirements. This paper reviews the latest research results in metal, carbon nanotube, and colloidal probes and reviews their related methods and techniques, analyses the advantages and disadvantages of the improved probes compared with ordinary probes by comparing the differences in spatial resolution, sensitivity, imaging, and other performance aspects, and finally provides an outlook on the future development of AFM probes. This paper promotes the development of AFM probes in the direction of new probes and further promotes the broader and deeper application of scanning probe microscope (SPM).

Novel dual-sensitization electrochemiluminescence immunosensor using photopermeable Ru(bpy)3 2+ -doped chitosan/SiO2 nanoparticles as labels and chitosan-decorated Nafion/MWNTs composites as enhancer

A novel dual-sensitization electrochemiluminescence (ECL) immunosensor for the detection of tumour protein prostate specific antigen (PSA) at trace level using Ru(bpy)₃ ²⁺ -doped chitosan/SiO₂ nanoparticles (Ru(bpy)₃ ²⁺ /chitosan/SiO₂ NPs) as the first signal enhancers was fabricated. Due to chitosan with excellent pore forming capacity, these nanoparticles possess porous structures and better photopermeability, and therefore have higher luminescence efficiencies compared with Ru(bpy)₃ ²⁺ /SiO₂ NPs reported in previous publications. Conversely, chitosan with good biocompatibility and high hydrophilicity was electrochemically decorated onto a Nafion/multiwall carbon nanotubes (Nafion/MWNTs) modified electrode surface and used as the second sensitizing matrix to seize large amounts of prostate specific capture antibody (Ab₁ ). The chitosan-decorated Nafion/MWNTs composites exhibited a 5.5-times higher ECL intensity than the unadorned Nafion/MWNTs films. Also, without additional reagents, such as (3-aminopropyl)triethoxysilane (APTS), the one-step functionalized Ru(bpy)₃ ²⁺ /chitosan/SiO₂ NPs provided a large number of active arms to connect with PSA-detected antibodies (Ab₂ ) through the amino groups in chitosan. After a sandwich immunoreaction, the PSA antigen and Ru(bpy)₃ ²⁺ /chitosan/SiO₂ NPs-labelled Ab₂ were sequentially captured onto the Ab₁ /chitosan/Nafion/MWNTs-modified electrode surface. The ECL signal increases were linearly related to the PSA antigen concentrations and ranged from 0.01 pg·mLl^-1 to 10.0 pg·mLl^-1 . Under the optimized experimental conditions, the immunosensor displayed excellent sensitivity and selectivity. The detection limit was as low as 3.4 fg·mLl^-1 , equivalent to, or better than, those of the reported ECL immunosensors for PSA.

A comprehensive review on the applications of nano-biosensor-based approaches for non-communicable and communicable disease detection

The outstretched applications of biosensors in diverse domains has become the reason for their attraction for scientific communities. Because they are analytical devices, they can detect both quantitative and qualitative biological components through the generation of detectable signals. In the recent past, biosensors witnessed significant changes and developments in their design as well as features. Nanotechnology has revolutionized sensing phenomena by increasing biodiagnostic capacity in terms of specificity, size, and cost, resulting in exceptional sensitivity and flexibility. The steep increase of non-communicable diseases across the world has emerged as a matter of concern. In parallel, the abrupt outbreak of communicable diseases poses a serious threat to mankind. For decreasing the morbidity and mortality associated with various communicable and non-communicable diseases, early detection and subsequent treatment are indispensable. Detection of different biological markers generates quantifiable signals that can be electrochemical, mass-based, optical, thermal, or piezoelectric. Speculating on the incumbent applicability and versatility of nano-biosensors in large disciplines, this review highlights different types of biosensors along with their components and detection mechanisms. Moreover, it deals with the current advancements made in biosensors and the applications of nano-biosensors in detection of various non-communicable and communicable diseases, as well as future prospects of nano-biosensors for diagnostics.

Diagnosis of cancer at early stages based on the multiplex detection of tumor markers using metal nanoclusters

Traditional cancer diagnosis strategies are not considered by most people until the last resort, which delays many cancer treatments leading to advanced stages. Tumor marker sensors show great potential for detecting cancer because of its cost-effective and harmless checking procedures. Normally, one tumor marker is detected each time by using one type of sensor, but the accuracy to declare cancer is not always satisfied. Metal nanoclusters are ultra-small nanomaterials with low toxicity, distinct optical properties, catalytic activities, and cost-effective performance. Some metal nanoclusters have been designed to detect more than one tumor marker in a single step. The consideration of combined parameters using such facile sensing strategies has the potential to simplify the test procedure, and increase the diagnostic accuracy of early cancer. Therefore, various sensing strategies for the multiplex detection of tumor markers using metal nanoclusters are summarized.

A novel"turn-off"fluorescence assay based on acid-copper nanoclusters in deep eutectic solvent micelles for co-aggregation inducing fluorescence enhancement and its application

As mixtures, deep eutectic solvent (DES) is designability. By adjusting the long alkyl chain hydrogen bond acceptors (HBAs) or hydrogen bond donors (HBDs), the DES displays surfactant characteristics and can form micelles. Hence, a novel, simple, facile and green natural organic acids capped copper nanoclusters (Aci-CuNCs) was synthesized and the spectrum behavior of Aci-CuNCs in DES micelles was researched. It was found that the surfactant-like DES can form micellar co-aggregation with Aci-CuNCs, resulting in the fluorescence (FL) intensive of Aci-CuNCs increase. Corresponding performance of spectral properties of Aci-CuNCs in DES medium were systematically studied by fourier transform infrared spectrometer, 3D FL spectroscopy, FL emission/excitation spectra, ultraviolet absorption spectroscopy. In the mechanism exploration part, on the one hand, the existence of micellar co-aggregation was confirmed by the conductivity, the mass effect of DES, dynamic light scattering and transmission electron microscopy. On the other hand, the influence of different kinds of DESs (types of HBAs/HBDs, molar ratio) and some possible factors (ionic strength and temperature) were discussed in detail to investigate the main driving forces for the formation of micellar co-aggregates. The results of mechanism exploration prove that the long alkyl chain of DES is amphiphilic which can form micellar co-aggregation with Aci-CuNCs through hydrogen bonding. The DES micelle provides Aci-CuNCs with a relatively stable and closed micro-environment which can effectively prevent collisions with water molecules and weakening of fluorescence intensity. On the basic of the above research, a "turn-off" fluorimetric method based on Aci-CuNCs in DES medium was applied for the determination of Fe³⁺. Under the optimum conditions, the assay worked in the Fe³⁺ concentration ranges from 1 to -20 μM and had a detection limit of 0.0374 μM. Method validation study illustrates the proposed system can provide a good accuracy, repeatability and stability conditions. Furthermore, the real sample analysis result demonstrates that no obvious matrix effect is found. As a consequence, the FL assays (Aci-CuNCs-based DES) composed of natural organic acid capped CuNCs and green solvent DES provides a simple, gentle and environmentally friendly method for the detection of iron ions.

Integrating gold nanoclusters, folic acid and reduced graphene oxide for nanosensing of glutathione based on "turn-off" fluorescence

Glutathione (GSH) is a useful biomarker in the development, diagnosis and treatment of cancer. However, most of the reported GSH biosensors are expensive, time-consuming and often require complex sample treatment, which limit its biological applications. Herein, a nanobiosensor for the detection of GSH using folic acid-functionalized reduced graphene oxide-modified BSA gold nanoclusters (FA-rGO-BSA/AuNCs) based on the fluorescence quenching interactions is presented. Firstly, a facile and optimized protocol for the fabrication of BSA/AuNCs is developed. Functionalization of rGO with folic acid is performed using EDC/NHS cross-linking reagents, and their interaction after loading with BSA/AuNCs is demonstrated. The formation of FA-rGO, BSA/AuNCs and FA-rGO-BSA/AuNCs are confirmed by the state-of-art characterization techniques. Finally, a fluorescence turn-off sensing strategy is developed using the as-synthesized FA-rGO-BSA/AuNCs for the detection of GSH. The nanobiosensor revealed an excellent sensing performance for the detection of GSH with high sensitivity and desirable selectivity over other potential interfering species. The fluorescence quenching is linearly proportional to the concentration of GSH between 0 and 1.75 µM, with a limit of detection of 0.1 µM under the physiological pH conditions (pH 7.4). Such a sensitive nanobiosensor paves the way to fabricate a "turn-on" or "turn-off" fluorescent sensor for important biomarkers in cancer cells, presenting potential nanotheranostic applications in biological detection and clinical diagnosis.

Aggregation-Induced Emission of Au/Ag Alloy Nanoclusters for Fluorescence Detection of Inorganic Pyrophosphate and Pyrophosphatase Activity

The development of sensitive and accurate detection of inorganic pyrophosphate (PPi) and pyrophosphatase activity (PPase) is important as they play vital roles in biological systems. However, it is still not satisfactory for most of the analytical methods for PPi and PPase because of their Cu²⁺-dependence and poor accuracy. Although the metal ion triggered aggregation-induced emission (AIE) of metal nanoclusters (NCs) offers a new approach to design a Cu²⁺-free strategy for the accurate determination of PPi and PPase recently, current methods are all focused on utilizing pure metal NCs. Alloy NCs incorporating the advantages of diverse metal usually can achieve improved behaviors in the application, such as enhanced sensitivity and stability. In this work, glutathione stabilized alloy Au/Ag NCs were synthesized via a simple method and used for the fluorescence detection of PPi and PPase based on a Zn²⁺-regulated AIE strategy. The controlled release of Zn²⁺ by PPi and PPase could regulate the AIE of Au/Ag NCs and be employed to response PPi concentration and PPase activity. This method processes simple procedure, high sensitivity and stability, and low toxicity. In addition, we also studied the AIE behaviors of this Au/Ag NCs and offer some fundamental understanding of the AIE properties of water-soluble alloy NCs. This study not only provides a straightforward and new approach for PPi and PPase determination but a basis for further study on the AIE properties of alloy NCs and their application.

Dual-modal label-free genosensor based on hemoglobin@gold nanocluster stabilized graphene nanosheets for the electrochemical detection of BCR/ABL fusion gene

For the first time, we have successfully synthesized stable graphene nanosheets from graphite powder through sonication in the hemoglobin-capped gold nanoclusters (Hb@AuNCs) solution for biosensing application. This approach, as a simple method for the exfoliation and fragmentation of graphite in a nanocluster solution, enabled us to produce stable aqueous graphene dispersions at low cost and without the need for hazardous chemicals or tedious experimental procedures. In this method, Hb@AuNCs were used not only as stabilizing agent of graphene through non-covalent bonding, but also as dispersing agent of few-layer graphene nanosheets. The Hb@AuNCs stabilized graphene (Hb@AuNCs-G) was characterized by high resolution transmission electron microscopy (HRTEM), zeta-sizer and Raman spectroscopy. Then, the graphene nanosheets were applied as a novel versatile electrochemical platform for ultrasensitive biosensing of short DNA species of chronic myelogenous leukemia (CML) based on the "signal off" and "signal on" strategies. For this purpose, a single strand DNA (ssDNA) was immobilized on the Hb@AuNCs-G/AuNPs modified electrode surface and acted as the biorecognition element. Methylene blue (MB), as the signaling probe, was then intercalated into the ssDNA. The intercalated MB was liberated upon interaction with the synthetic complementary DNA (cDNA, target), thereby resulting in the apparent reduction of MB redox signal. This designed "signal off" sensing system enabled the voltammetric determination of the target cDNA over a dynamic linear range (DLR) of 0.1 fM to 10 pM with a limit of detection (LOD) of 0.037 fM. In the "signal on" strategy, the response to the cDNA was detected by monitoring the change in the electron transfer resistance (R_ct) using the ferro/ferricyanide system as a redox probe. The charge transfer resistance of the probe was found to increase linearly with increasing concentration of target cDNA in the range of 0.1 fM-10 pM with a limit of detection of 0.030 fM. Finally, the selectivity and feasibility of genosensor was evaluated by the analysis of derived nucleotides from mismatched sequences and the clinical samples of patients with leukemia as real samples, respectively.