Overview of the Design and Application of Photothermal Immunoassays

Developing powerful immunoassays for sensitive and real-time detection of targets has always been a challenging task. Due to their advantages of direct readout, controllable sensing, and low background interference, photothermal immunoassays have become a type of new technology that can be used for various applications such as disease diagnosis, environmental monitoring, and food safety. By modification with antibodies, photothermal materials can induce temperature changes by converting light energy into heat, thereby reporting specific target recognition events. This article reviews the design and application of photothermal immunoassays based on different photothermal materials, including noble metal nanomaterials, carbon-based nanomaterials, two-dimensional nanomaterials, metal oxide and sulfide nanomaterials, Prussian blue nanoparticles, small organic molecules, polymers, etc. It pays special attention to the role of photothermal materials and the working principle of various immunoassays. Additionally, the challenges and prospects for future development of photothermal immunoassays are briefly discussed.

Application of photothermal effects of nanomaterials in food safety detection

Numerous nanomaterials endowed with outstanding light harvesting and photothermal conversion abilities have been extensively applied in various fields, such as photothermal diagnosis and therapy, trace substance detection, and optical imaging. Although photothermal detection methods have been established utilizing the photothermal effect of nanomaterials in recent years, there is a scarcity of reviews regarding their application in food safety detection. Herein, the recent advancements in the photothermal conversion mechanism, photothermal conversion efficiency calculation, and preparation method of photothermal nanomaterials were reviewed. In particular, the application of photothermal nanomaterials in various food hazard analyses and the newly established photothermal detection methods were comprehensively discussed. Moreover, the development and promising future trends of photothermal nanomaterial-based detection methods were discussed, which provide a reference for researchers to propose more effective, sensitive, and accurate detection methods.

Ascorbic Acid-Mediated in situ Growth of Gold Nanostars for Photothermal Immunoassay of Ochratoxin A

Currently, the development of efficient mycotoxins detection methods, particularly using portable devices as readout devices, remains a great challenge. Herein, a photothermal enzyme-linked immunosorbent assay (ELISA) based on gold nanostars (AuNSs) for the detection of ochratoxin A (OTA) using a "thermometer" was proposed for the first time. AuNSs with photothermal conversion capacity were parepared using an ascorbic acid (AA)-mediated in situ growth methd. Quantification was based on the alkaline phosphatase catalyzing the dephosphorylation of ascorbic acid 2-phosphoate to AA, thereby converting OTA concentration to the amount of in situ synthesized AuNSs, thus achieving straightforward readout by temperature. Benefiting from the classical tyramine signal amplification strategy, a detection limit of 0.39 ng mL^-1 was obtained. The recoveries of grape juice and maize samples spiked with 10 ng mL^-1 and 30 ng mL^-1 OTA ranged from 86.53% to 116.9%. Our method has great potential in on-site OTA detection for food safety.

A polypyrrole-mediated photothermal biosensor with a temperature and pressure dual readout for the detection of protein biomarkers

A novel photothermal biosensor with a temperature and pressure dual readout was developed for CRP detection. The in situ synthesized polypyrrole exhibits photothermal effect under NIR light to increase temperature and pressure for portable readout.

Aptamer based surface plasma resonance assay for direct detection of neuron specific enolase and progastrin-releasing peptide (31-98)

Neuron specific enolase (NSE) and progastrin-releasing peptide (31-98) (ProGRP31-98) are considered as reliable biomarkers of small cell lung cancer (SCLC). Sensitive determinations of NSE and ProGRP31-98 show great significance in disease surveillance, clinical diagnosis, efficacy evaluation and prognostic judgment. However, the conventional detection methods have the disadvantages of poor stability, tedious operation, and being very time consuming. Herein, we developed an aptamer-based surface plasmon resonance (SPR) assay in a direct format for NSE and ProGRP31-98 detection. The aptamer was loaded on a sensor chip and used as an affinity ligand. With sample injection, SPR signals increased due to the association of the target to the aptamer coated chip. Further dissociation and regeneration allowed this aptamer sensor chip to be used for the next sample analysis. We achieved sensitive detection of NSE and ProGRP31-98 by measuring the affinity binding-induced SPR responses. The detection limits for NSE and ProGRP31-98 were 3.9 nM and 15.6 nM, respectively. The aptamer sensor chip is stable and reusable, and has potential for diluted human serum analysis. This assay presents strengths in simplicity, rapidity, low material consumption, real time analysis and ease of implementing high throughput and automatic detection. It is promising for application in clinical disease-related biomarkers analysis.

A sensitive photothermometric biosensor based on redox reaction-controlled nanoprobe conversion from Prussian blue to Prussian white

As a new low-cost photothermal nanoprobe, Prussian blue nanoparticles (PB NPs) have been demonstrated to have more potential in photothermometric-based point-of-care testing (POCT) application. However, most of the existing PB NP-based photothermometric sensors were constructed mainly relying on in situ generation of PB NPs or their combination with antigens and antibodies, therefore usually suffering from the inherent defects like complicated preparation and cumbersome surface process as well as high-cost modification. To break this limitation of PB NP-based photothermometric POCT, we proposed an ingenious redox reaction-controlled nanoprobe conversion strategy and successfully applied to photothermometric detection of ascorbate oxidase (AAO). In this design, the heat of PB NP photothermal system under 808-nm laser irradiation dramatically decreased with the addition of AA, due to a unique AA-induced Prussian blue to Prussian white (PB-to-PW) conversion. Upon AAO addition, the heat of reaction system increased because of the enzymatic catalytic reaction between AAO and AA, which led to a significant reduction of AA and resultantly inhibited PB-to-PW conversion. Such target-mediated nanoprobe conversion resulted in an obvious temperature change that could be easily detected by a common thermometer and exhibited good linear ranges from 0.25 to 14 mU/mL with a detection limit as low as 0.21 mU/mL for POCT analysis of AAO. This facile, convenient, and portable photothermometric sensing platform provides an innovative route for the design of PB NP nanoprobe-based photothermometric detection methods. A sensitive photothermometric AAO sensor based on a redox reaction-controlled nanoprobe conversion strategy from Prussian blue to Prussian white.

Liposome-assisted enzyme catalysis: toward signal amplification for sensitive split-type electrochemiluminescence immunoassay

Developing an efficient signal amplification strategy is very important to improve the sensitivity of bioanalysis. In this paper, a liposome-assisted enzyme catalysis signal amplification strategy was developed for electrochemiluminescence (ECL) immunoassay of prostate specific antigen (PSA) in a split-type mode. The sandwich immunoreaction occurred in a 96-well plate, and glucose oxidase (GOx) encapsulated and antibody-modified liposomes were used as labels. The ECL detection was carried out using a rGO-Au NP modified glassy carbon electrode (GCE). The large amount of generated H2O2, i.e. the coreactant of the luminol system, and the excellent catalytic behavior of rGO-Au NPs greatly boosted the ECL signal, resulting in the signal amplification. The developed ECL immunosensor for detecting PSA achieved a wider linear range from 1.0 × 10-13 to 1.0 × 10-8 g mL-1 and a detection limit of 1.7 × 10-14 g mL-1. The application of the proposed strategy was demonstrated by analyzing PSA in human serum samples with recoveries from 89.0% to 113.0%, and relative standard deviations (RSDs) were less than 6.6%. This work provides a new horizon to expand the application of liposomes for ECL bioanalysis.

"Dual Signal-On" Split-Type Aptasensor for TNF-α: Integrating MQDs/ZIF-8@ZnO NR Arrays with MB-Liposome-Mediated Signal Amplification

Ultrasensitive and accurate detection of biomarkers in serum is of great importance for disease diagnosis and treatment. So far, the commonly used single-mode signal suffers from certain instinct drawbacks that restrict assay performances. Herein, we report the proof-of-concept fabrication of a split-type photoelectrochemical (PEC) and electrochemical (EC) dual-modal aptasensor for ultrasensitively tracing tumor necrosis factor-α, a noteworthy biological biomarker with essential clinical importance. By smart integrating molybdenum disulfide QDs/zeolitic imidazolate framework-8@ZnO nanorod arrays with a methylene blue-liposome-mediated signal amplification strategy, "dual signal-on" detection is accomplished based on a sandwich reaction of the target with aptamer-anchored carboxyl magnetic beads and an aptamer-confined MB liposome. Linear ranges of 5 fg/mL-5 μg/mL (detection limit 1.46 fg/mL) for PEC and 10 fg/mL-0.5 μg/mL (detection limit 6.14 fg/mL) for EC are obtained, respectively. An independent signal transduction mechanism supports the accuracy improvement, and a separate biological process from a translator enables convenient fabrication, short-time consumption, wider linearity, as well as outstanding reproducibility and stability in practical application. This work presents a universal bioassay route with prospects in biomedical and related areas.

A three-dimensional CoNi-MOF nanosheet array-based immunosensor for sensitive monitoring of human chorionic gonadotropin with core-shell ZnNi-MOF@Nile Blue nanotags

A CoNi-based metal-organic framework (CoNi-MOF) nanosheet array is synthesized by the treatment of a CoNi layered double hydroxide nanosheet array on Ni foam with 3,5-diaminobenzoic acid. The CoNi-MOF nanosheet array with amino and carboxyl groups can be used to capture the human chorionic gonadotropin (HCG) primary antibody (HCG Ab1). Nile Blue decorated ZnNi-MOF (NB@ZnNi-MOF) spheres immobilized with HCG secondary antibodies (HCG Ab2) are used for signal amplification. When HCG exists in an analytical sample, a sandwich structure is formed and an electrochemical signal is produced. The analytical signal generated during the detection is caused by the conversion of Co(ii) and Co(iii) in the CoNi-MOF nanosheet array. The Nile Blue of the NB@ZnNi-MOF sphere, as a kind of redox-active species, is responsible for the electrochemical signal amplification in the immunosensor. On the basis of the above advantages, the HCG immunosensor exhibits a lower limit of detection (1.85 × 10-3 mIU mL-1) and a wide linear range from 0.005 mIU mL-1 to 250 mIU mL-1. Additionally, this immunosensor is used to quantitatively detect HCG in human blood serum and shows good correlations with the standard enzyme-linked immunosorbent assay (ELISA), providing a high value on clinical diagnosis.

Gefitinib encapsulation based on nano-liposomes for enhancing the curative effect of lung cancer

Gefitinib (GEB) is one of the drugs used for patients with epidermal growth factor receptor (EGFR)-positive mutations in non-small cell lung cancer (NSCLC). However, application of GEB is limited by its low water solubility, stability, and utilization rate, especially the side effects while GEB is given by oral. In this study, nanoliposome was used as a carrier to prepare nanoliposome compound drug (GL) by embedding GEB in the nanoliposome perfectly combined with green nontoxic solvent and thin-film dispersion method. The nanoliposome structure was expected to improve the water solubility and biocompatibility of GEB, thus improving the effect of cancer treatment. The surface electronegative nanoliposomes can effectively avoid protein adsorption and prolong the circulation time in vivo. Meanwhile, the ratio of lecithin to cholesterol (LE/CH) was explored to maximize the encapsulation efficiency of nanoliposome. Subsequent test results showed that GL exhibited better stability, smaller particle size and higher encapsulation efficiency. In addition, in vitro drug release curve also further confirmed that GL had a promising drug sustained-release effect. In particular, a series of in vitro tests such as cell activity, apoptosis, colony formation, scratch, invasion, and cell cycle assays were performed. The results indicated that GL significantly enhanced the pro-apoptotic effect on A549 cells. Most cell cycles of A549 cells were blocked in the G0/G1 phase influenced by GL, thus inhibiting the proliferation of cancer cells. In vivo anti-tumor studies showed that compared with pure GEB, GL had a significant inhibiting effect on NSCLC. In conclusion, the GL which was synthesized by a simple method in this study significantly improved the treatment effect of cancer cells, which proved that the nanoliposome carrier had an excellent application prospect in the treatment of lung cancer.

Ultrasensitive electrochemical detection of neuron-specific enolase based on spiny core-shell Au/CuxO@CeO2 nanocubes

As a specific biomarker, neuron-specific enolase (NSE) is an essential clinical indicator for diagnosing small cell lung cancer. In this paper, a sandwich-type electrochemical immunosensor was designed for the quantitative detection of NSE. AuPt nanoblock spherical nanoarchitectonics (AuPt NSNs), a bimetallic nanoparticle with a rugged morphology, were utilized as the substrate, which could enhance the electronic conduction and increase the immobilization capacity of the primary antibody (Ab₁). Moreover, through a simple hydrothermal method, Au/Cu_xO@CeO₂ was prepared as a spiny core-shell nanocube with cerium dioxide (CeO₂) and gold nanoparticles (Au NPs) loading. The combination of Cu₂O, CuO, and CeO₂ showed favorable catalytic activity toward hydrogen peroxide (H₂O₂). Furthermore, the deposition of Au NPs on the spiny surface structure enhanced the specific surface area and biocompatibility, thereby rendering it more effective for loading the second antibody (Ab₂). As the label material, the Au/Cu_xO@CeO₂ achieved signal amplification and sensitive detection with the immunosensor. Under optimal conditions, the designed immunosensor possessed a broad linear range of 50 fg mL^-1 to 100 ng mL^-1 and a limit of detection of 31.3 fg mL^-1, along with satisfactory performance in sensitivity, selectivity, and stability.

Au-coated Fe3O4 core-shell nanohybrids with photothermal activity for point-of-care immunoassay for lipoprotein-associated phospholipase A2 on a digital near-infrared thermometer

A portable photothermal immunoassay based on Au-coated magnetic Fe₃O₄ core-shell nanohybrids (Au-Fe₃O₄) was developed for point-of-care (POC) testing of lipoprotein-associated phospholipase A₂ (Lp-PLA₂) on a digital near-infrared (NIR) thermometer. Au-Fe₃O₄ photothermal materials were first synthesized through reverse micelle method, and then functionalized with polyclonal rabbit anti-human Lp-PLA₂ antibody. A sandwiched immunoreaction was carried out in polyclonal mouse anti-human Lp-PLA₂ antibody-coated microplate using Au-Fe₃O₄-labeled antibody as the detection antibody. With formation of sandwich-type immunocomplex, the captured Au-Fe₃O₄ on the plate converted the light into heat under an 808-nm laser irradiation (1.5 W cm^-2), thereby resulting in the increasing temperature of the detection solution. The temperature variations relative to surrounding temperature was determined on a portable NIR thermometer. Several labeling protocols with gold nanoparticle, Fe₃O₄ nanoparticle, or Au-Fe₃O₄ nanohybrids were investigated for determination of Lp-PLA₂ and improved analytical features were achieved with the core-shell Au-Fe₃O₄ nanohybrids. Under optimum conditions, Au-Fe₃O₄-based immunoassay exhibited good photothermal responses for the detection of Lp-PLA₂ with a dynamic linear range of 0.01-100 ng mL^-1 at a low detection limit of 8.6 pg mL^-1. Good reproducibility and intermediate precision were less than 9.7%. Other biomarkers or proteins did not interfere with responses of this system. An acceptable accuracy was acquired for analysis of human serum sample between Au-Fe₃O₄-based photothermal immunoassay and commercialized human Lp-PLA₂ ELISA kit.