Stable and Photothermally Efficient Antibody-Covered Cu3(PO4)2@Polydopamine Nanocomposites for Sensitive and Cost-Effective Immunoassays

Integrated biosensor array for multiplex biomarkers cancer diagnosis via in-situ self-assembly carbon nanotubes with an ordered inverse-opal structure

To enhance the precision and reliability of early disease detection, especially in malignancies, an exhaustive investigation of multi-target biomarkers is essential. In this study, an advanced integrated electrochemical biosensor array that demonstrates exceptional performance was constructed. This biosensor was developed through a controllable porous-size mechanism and in-situ modification of carbon nanotubes (CNTs) to quantify multiplex biomarkers-specifically, C-reaction protein (CRP), carbohydrate antigen 125 (CA125), and carcinoembryonic antigen (CEA)-in human serum plasma. The fabrication process involved creating a highly ordered three-dimensional inverse-opal structure with the CNTs (pCNTs) modifier through microdroplet-based microfluidics, confined spatial self-assembly of nanoparticles, and chemical wet-etching. This innovative approach allowed for direct in-situ modification of nanomaterial onto the surface of electrode array, eliminating secondary transfer and providing exceptional control over structure and stability. The outstanding electrochemical performance was achieved through the synergistic effect of the pCNTs nanomaterial, aptamer, and horseradish peroxidase-labeled (HRP-) antibody. Additionally, the integrated biosensor array platform comprised multiple individually addressable electrode units (n = 11), enabling simultaneous multi-parallel/target testing, thereby ensuring accuracy and high throughput. Crucially, this integrated biosensor array accurately quantified multiplex biomarkers in human serum, yielding results comparable to commercial methods. This integrated technology holds promise for point-of-care testing (POCT) in early disease diagnosis and biological analysis.

Dual-mode fluorescence and colorimetric smartphone-based sensing platform with oxidation-induced self-assembled nanoflowers for sarcosine detection

BACKGROUND

Early prostatic cancer (PCa) diagnosis significantly improves the chances of successful treatment and enhances patient survival rates. Traditional enzyme cascade-based early cancer detection methods offer efficiency and signal amplification but are limited by cost, complexity, and enzyme dependency, affecting stability and practicality. Meanwhile, sarcosine (Sar) is commonly considered a biomarker for PCa development. It is essential to develop a Sar detection method based on cascade reactions, which should be efficient, low skill requirement, and suitable for on-site testing.

RESULTS

To address this, our study introduces the synthesis of organic-inorganic self-assembled nanoflowers to optimize existing detection methods. The Sar oxidase (SOX)-inorganic hybrid nanoflowers (Cu3(PO4)2:Ce@SOX) possess inherent fluorescent properties and excellent peroxidase activity, coupled with efficient enzyme loading. Based on this, we have developed a dual-mode multi-enzyme cascade nanoplatform combining fluorescence and colorimetric methods for the detection of Sar. The encapsulation yield of Cu3(PO4)2:Ce@SOX reaches 84.5 %, exhibiting a remarkable enhancement in catalytic activity by 1.26-1.29 fold compared to free SOX. The present study employing a dual-signal mechanism encompasses 'turn-off' fluorescence signals ranging from 0.5 μM to 60 μM, with a detection limit of 0.226 μM, and 'turn-on' colorimetric signals ranging from 0.18 μM to 60 μM, with a detection limit of 0.120 μM.

SIGNIFICANCE

Furthermore, our study developed an intelligent smartphone sensor system utilizing cotton swabs for real-time analysis of Sar without additional instruments. The nano-platform exhibits exceptional repeatability and stability, rendering it well-suited for detecting Sar in authentic human urine samples. This innovation allows for immediate analysis, offering valuable insights for portable and efficient biosensors applicable to Sar and other analytes.

Recent advances in photothermal nanomaterials-mediated detection of circulating tumor cells

Photothermal materials have shown great potential for cancer detection and treatment due to their excellent photothermal effects. Circulating tumor cells (CTCs) are tumor cells that are shed from the primary tumor into the blood and metastasize. In contrast to other tumor markers that are free in the blood, CTCs are a collective term for all types of tumor cells present in the peripheral blood, a source of tumor metastasis, and clear evidence of tumor presence. CTCs detection enables early detection, diagnosis and treatment of tumors, and plays an important role in cancer prevention and treatment. This review summarizes the application of various photothermal materials in CTC detection, including gold, carbon, molybdenum, phosphorus, etc. and describes the significance of CTC detection for early tumor diagnosis and tumor prognosis. Focus is also put on how various photothermal materials play their roles in CTCs detection, including CT, imaging and photoacoustic and therapeutic roles. The physicochemical properties, shapes, and photothermal properties of various photothermal materials are discussed to improve the detection sensitivity and efficiency and to reduce the damage to normal cells. These photothermal materials are capable of converting radiant light energy into thermal energy for highly-sensitive CTCs detection and improving their photothermal properties by various methods, and have achieved good results in various experiments. The use of photothermal materials for CTCs detection is becoming more and more widespread and can be of significant help in early cancer screening and later treatment.

Phenolic Ligand-Metal Charge Transfer Induced Copper Nanozyme with Reactive Oxygen Species-Scavenging Ability for Chronic Wound Healing

Chronic wounds frequently arise as a complication in diabetic patients, and their management remains a significant clinical hurdle due to their nonhealing nature featured by heightened oxidative stress and impaired healing cells at the wound site. Herein, we present a 2D copper antioxidant nanozyme induced by phenolic ligand-metal charge transfer (LMCT) to eliminate reactive oxygen species (ROS) and facilitate the healing of chronic diabetic wounds. We found that polyphenol ligands coordinated on the Cu3(PO4)2 nanosheets led to a strong charge transfer at the interface and regulated the valence states of Cu. The obtained Cu nanozyme exhibited efficient scavenging ability toward different oxidative species and protected human cells from oxidative damage. The nanozyme enhanced the healing of diabetic wounds by promoting re-epithelialization, collagen deposition, angiogenesis, and immunoregulation. This work demonstrates the LMCT-induced ROS scavenging ability on a nanointerface, providing an alternative strategy of constructing metal-based nanozymes for the treatment of diabetic wounds as well as other diseases.

Vertically oriented SnS2 on MoS2 nanosheets for high-photoresponsivity and fast-response self-powered photoelectrochemical photodetectors

Van der Waals heterostructures have great potential for the emerging self-powered photoelectrochemical photodetectors due to their outstanding photoelectric conversion capability and efficient interfacial carrier transportation. By considering the band alignment, structural design, and growth optimization, the heterostructures of vertically oriented SnS₂ with different densities on MoS₂ nanosheets are designed and fabricated using a two-step epitaxial growth method. Compared with SnS₂, MoS₂, and low density-vertical SnS₂/MoS₂ heterostructure, the high density-vertical SnS₂/MoS₂ heterostructure exhibits largely enhanced self-powered photodetection performances, such as a giant photocurrent density (∼932.8 μA cm^-2), an excellent photoresponsivity (4.66 mA W^-1), and an ultrafast response/recovery time (3.6/6.4 ms) in the ultraviolet-visible range. This impressive enhancement of high density-vertical SnS₂/MoS₂ photodetectors is mainly ascribed to the essentially improved charge transfer and carrier transport of type-II band alignment heterostructures and the efficient light absorption from the unique light-trapping structure. In addition, the photoelectrocatalytic water splitting performance of the high density-vertical SnS₂/MoS₂ heterostructure also benefits from the type-II band alignment and the light-trapping structure. This work provides valuable inspiration for the design of two-dimensional optoelectronic and photoelectrochemical devices with improved performance by the morphology and heterostructure design.

Strategies to simplify operation procedures for applying labeled antibody-based immunosensors to point-of-care testing

Point-of-care testing (POCT) is an ideal testing format for the rapid and on-site detection of analytes in patients, and facilitates disease diagnosis and monitoring. Molecular recognition elements are required for the specific detection of analytes, and biosensors that use antibodies as the molecular recognition elements are called immunosensors. Traditional immunosensors such as sandwich enzyme-linked immunosorbent assay (ELISA) require complicated procedures to form immunocomplexes consisting of detection antibodies, analytes, and capture antibodies. They also require long incubation times, washing procedures, and large and expensive specialized equipment that must be operated by laboratory technicians. Immunosensors for POCT should be systems that use relatively small pieces of equipment and do not require special training. In this review, to help in the construction of immunosensors for POCT, we have summarized the recently reported strategies for simplifying the operation, incubation, and washing procedures. We focused on the optical and electrochemical detection principles of immunosensors, compared the strategies for operation, sensitivity, and detection devices and discussed the ideal system. Combining detection devices that can be fabricated inexpensively and strategies that enable simplification of operation procedures and enhance sensitivities will contribute to the development of immunosensors for POCT.

Dumbbell-Shaped Ternary Transition-Metal (Cu, Ni, Co) Phosphate Bundles: A Promising Catalyst for the Oxygen Evolution Reaction

Development of economical and high-performance electrocatalysts for the oxygen evolution reaction (OER) is of tremendous interest for future applications as sustainable energy materials. Here, a unique member of efficient OER electrocatalysts has been developed based upon structurally versatile dumbbell-shaped ternary transition-metal (Cu, Ni, Co) phosphates with a three-dimensional (3D) (Cu₂(OH)(PO₄)/Ni₃(PO₄)₂·8H₂O/Co₃(PO₄)₂·8H₂O) (CNCP) structure. This structure is prepared using a simple aqueous stepwise addition of metal ion source approach. Various structural investigations demonstrate highly crystalline nature of the composite structure. Apart from the unique structural aspect, it is important that the CNCP composite structure has proved to be an excellent electrocatalyst for OER performance in comparison with its binary or constituent phosphate under alkaline and neutral conditions. Notably, the CNCP electrocatalyst displays a much lower overpotential of 224 mV at a current density of 10 mA cm^-2 and a lower Tafel slope of 53 mV dec^-1 with high stability in alkaline medium. In addition, X-ray photoelectron spectroscopy analysis suggested that the activity and long-term durability for the OER of the ternary 3D metal phosphate are due to the presence of electrochemically dynamic constituents such as Ni and Co and their resulting synergistic effects, which was further supported by theoretical studies. Theoretical calculations also reveal that the incredible OER execution was ascribed to the electron redistribution set off in the presence of Ni and Cu and the most favorable interaction between the *OOH intermediate and the active sites of CNCP. This work may attract the attention of researchers to construct efficient 3D ternary metal phosphate catalysts for various applications in the field of electrochemistry.

NIR II Light-Response Au Nanoframes: Amplification of a Pressure- and Temperature-Sensing Strategy for Portable Detection and Photothermal Therapy of Cancer Cells

Quantitative detection of cancer cells using portable devices is promising for the development of simple, fast, and point-of-care cancer diagnostic techniques. However, how to further amplify the detection signal to improve the sensitivity and accuracy of detecting cancer cells by portable devices remains a challenge. To solve the problem, we, for the first time, synthesized folic-acid-conjugated Au nanoframes (FA-Au NFs) with amplification of pressure and temperature signals for highly sensitive and accurate detection of cancer cells by portable pressure meters and thermometers. The resulting Au NFs exhibit excellent near-infrared (NIR) photothermal performance and catalase activity, which can promote the decomposition of NH₄HCO₃ and H₂O₂ to generate corresponding gases (CO₂, NH₃, and O₂), thereby synergistically amplifying pressure signals in a closed reaction vessel. At the same time, Au NFs with excellent peroxidase-like activity can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to produce TMB oxide (oxTMB) with a strong photothermal effect, thereby cooperating with Au NFs to amplify the photothermal signal. In the presence of cancer cells with overexpressing folate receptors (FRs), the molecular recognition signals between FA and FR can be converted into amplified pressure and temperature signals, which can be easily read by portable pressure meters and thermometers, respectively. The detection limits for cancer cells using pressure meters and thermometers are 6 and 5 cells/mL, respectively, which are better than other reported methods. Moreover, such Au NFs can improve tumor hypoxia by catalyzing the decomposition of H₂O₂ to produce O₂ and perform photothermal therapy of cancer. Together, our work provides new insight into the application of Au NFs to develop a dual-signal sensing platform with amplification of pressure and temperature signals for portable and ultrasensitive detection of cancer cells as well as personalized cancer therapy.

A portable thermal detection method based on the target responsive hydrogel mediated self-heating of a warming pad

A simple thermal aptasensing platform was devised for the sensitive detection of organophosphate pesticides (using malathion as a model target) based on the efficient self-heating reaction of a warming pad with a switchable target responsive enzyme-encapsulated three-dimensional (3D) DNA hydrogel using a portable thermometer as a signal readout in this work. The existence of the target malathion would open the catalase-3D network and lots of catalase was released from the hydrogel, which could efficiently convert H₂O₂ to an O₂ molecule. The product O₂ is the critical condition for the self-heating of the warming pad. Thereafter, the temperature was enhanced with the increasing amount of O₂. The strategy displays outstanding specificity, reproducibility and stability. Moreover, this method can be easily extended to monitor other molecules using different aptamer sequences in practical applications.

Portable and quantitative detection of carbendazim based on the readout of a thermometer

The detection of carbendazim (CBZ) is important for food safety and human health. However, most current analytical methods require large instruments and highly trained operators. In order to solve this problem, herein, an innovative portable and quantitative photothermal assay platform relying on a thermometer readout for the detection of CBZ has been developed. Gold nanoparticles (AuNPs), which exhibit a strong distance-dependent photothermal effect under specific laser irradiation, were utilized as indicators. The CBZ aptamer was introduced to protect AuNPs from salt-mediated aggregation. When CBZ is present, the binding event between CBZ and aptamer leads to the loss of the aptamer protective effect on AuNPs, and AuNP aggregation occurs. Under 650-nm laser irradiation, the increase in temperature associated with an AuNP-dependent photothermal effect is highly related to the CBZ concentration. Having the advantages of user-friendliness, low cost, quick response, and portability, this method has great potential for on-site applications.

Enzyme/Nanocopper Hybrid Nanozymes: Modulating Enzyme-like Activity by the Protein Structure for Biosensing and Tumor Catalytic Therapy

Artificial enzymes with modulated enzyme-mimicking activities of natural systems represent a challenge in catalytic applications. Here, we show the creation of artificial Cu metalloenzymes based on the generation of Cu nanoparticles in an enzyme matrix. Different enzymes were used, and the structural differences between the enzymes especially influenced the controlled the size of the nanoparticles and the environment that surrounds them. Herein, we demonstrated that the oxidase-like catalytic activity of these copper nanozymes was rationally modulated by enzyme used as a scaffold, with a special role in the nanoparticle size and their environment. In this sense, these nanocopper hybrids have confirmed the ability to mimic a unique enzymatic activity completely different from the natural activity of the enzyme used as a scaffold, such as tyrosinase-like activity or as Fenton catalyst, which has extremely higher stability than natural mushroom tyrosinase. More interestingly, the oxidoreductase-like activity of nanocopper hybrids was cooperatively modulated with the synergistic effect between the enzyme and the nanoparticles improving the catalase activity (no peroxidase activity). Additionally, a novel dual (metallic and enzymatic activity) of the nanozyme made the highly improved catechol-like activity interesting for the design of 3,4-dihydroxy-l-phenylalanine (l-DOPA) biosensor for detection of tyrosinase. These hybrids also showed cytotoxic activity against different tumor cells, interesting in biocatalytic tumor therapy.

Four-Channel Photothermal Plate Reader for High-Throughput Nanoparticle-Amplified Immunoassay

We enhanced the sample throughput of microplate-based photothermal detection by using a semicylindrical prism to expand a point laser source to a long beam for illuminating multiple wells. Coupled with four epoxy-coated thermocouples in alignment with wells on a 96-well microplate, four parallel immunoassays of C-reaction protein (CRP) with antibody-conjugated gold nanoparticles can be simultaneously performed. The sample throughput is further increased by mounting the Styrofoam-enclosed microplate onto a translational/elevator stage so that immunoassays and thermocouple rinse/drying cycles can be implemented in a programmed fashion. The automated assay with three rinse/drying cycles takes only 34.5 min for four samples or 8.62 min/sample, whereas the manual mode with a single thermocouple and a point light source requires at least 66 min for just one sample. With careful calibration of the energy distribution of the expanded laser beam and controllable immersion of the thermocouples, excellent well-to-well (RSD = 1.3%) and cycle-to-cycle (RSD = 4.0%) reproducibility can be attained. The temperature changes can be correlated with the CRP concentration by the Langmuir isotherm, and the low limit of detection, 0.52 ng/mL or 4.33 pM, is well below the plasma CRP levels of both healthy people (<5 μg/mL) and patients (10-500 μg/mL). The serum CRP concentrations quantified by our plate reader are in excellent agreement with the immunoturbidimetric results, demonstrating that this cost-effective, robust, and high-throughput mode for microplate-based immunoassays is amenable to detecting biomarkers in many clinical samples.

Redox Switchable Polydopamine-Modified AFM-SECM Probes: A Probe for Electrochemical Force Spectroscopy

Polydopamine (PDA) has high potential in biorelevant applications as a versatile thin film material, e.g., as adhesive coating for cell immobilization or for sensing applications due to the plethora of functional groups. In this study we present the modification of conductive colloidal atomic force-scanning electrochemical microscopy (AFM-SECM) probes with electrochemically deposited PDA resulting in functional probes for quantitative electrochemical adhesion studies. Surface functionality of PDA can be altered by oxidation or reduction of functional groups applying an appropriate potential to the PDA-modified AFM-SECM probe, thereby enabling adhesion measurements under potential control. This facilitates probing specific interactions of surface groups present in PDA with various surfaces of different wettabilities. The versatility of such switchable AFM-SECM probes is demonstrated for electrochemical force spectroscopic studies at model samples such as plasma-treated gold substrates, hydrophobic or hydrophilic self-assembled monolayers, and for adhesion measurements of bacteria in dependence of altered surface charges of the colloidal probe. The maximum obtained adhesion force of a positively polarized PDA-modified AFM-SECM probe was 6.2 ± 2.2 nN, and it was about 50% less (i.e., 2.6 ± 1.1 nN) for a negatively polarized probe at a hydrophilic OH-terminated gold surface. In situ control of the active surface groups enabled investigations on the influence of surface charges on adhesion. Furthermore, plateaus of constant force were observed, which are a characteristic of polymer structures. Finally, electrochemical force measurements with switchable probes were used for the first time during adhesion studies of bacterial cells (i.e., Pseudomonas fluorescens). Positively biased PDA-coated colloidal probes revealed adhesion forces of 6.0 ± 1.1 nN, whereas significantly reduced adhesion forces 1.1 ± 0.7 nN were observed for negatively biased PDA-modified colloidal probes.