Ultrasensitive electrochemical sensor based on synergistic effect of Ag@MXene and antifouling cyclic multifunctional peptide for PD-L1 detection in serum.

A sensing interface co-constructed from the two-dimensional conductive material (Ag@MXene) and an antifouling cyclic multifunctional peptide (CP) is described. While the large surface area of Ag@MXene loads more CP probes, CP binds to Ag@MXene to form a fouling barrier and ensure the structural rigidity of the targeting sequence. This strategy synergistically enhances the biosensor's sensitivity and resistance to contamination. The SPR results showed that the binding affinity of the CP to the target was 6.23 times higher than that of the antifouling straight-chain multifunctional peptide (SP) to the target. In the 10 mg/mL BSA electrochemical fouling test, the fouling resistance of Ag@MXene + CP (composite sensing interface of CP combined with Ag@MXene) was 30 times higher than that of the bare electrode. The designed electrochemical sensor exhibited good selectivity and wide dynamic response range at PD-L1 concentrations from 0.1 to 50 ng/mL. The lowest detection limit was 24.54 pg/mL (S/N = 3). Antifouling 2D materials with a substantial specific surface area, coupled with non-straight chain antifouling multifunctional peptides, offer a wide scope for investigating the sensitivity and antifouling properties of electrochemical sensors.

Tunable Au@SiO2/Au Film Metasurface as Surface Plasmon Resonance Enhancer for Direct and Ultrasensitive Detection of Exosomes.

Surface plasmon resonance (SPR) spectroscopy with non-labelling, sensitive, and real-time properties is critical for clinical diagnosis applications. However, conventional SPR sensors face the challenge of lower sensitivity and selectivity for trace exosomes assay in complex serum. We proposed a core-shell Au@SiO2-Au film (Au@SiO2-Au film) metasurface to enhance SPR signal based on systematic study on the relationship between gap modes and SPR enhancement. The self-assembled multifunctional peptide was designed as recognition layer with antifouling properties for ultrasensitive and selective detection of PD-L1+ exosomes in serum. The tuning electromagnetic (EM) field model by manipulating the gap was established to guide the preparation of Au@SiO2-Au film metasurface. The in-plane and out-of-plane coupling of Au@SiO2 nanoparticles (NPs) could greatly enlarge and enhance three-dimensional EM field to meet the size of exosomes located in the evanescent field. At the structural level, we achieved high sensitivity (0.16 particles/mL) and a broad response range (10-5 × 103 particles/mL) through optimizing the thickness of SiO2 and surface coverage of Au@SiO2. Furthermore, clinical sample assay achieved the optimal diagnostic accuracy (AUC = 0.97) for differentiating cancer patients from healthy controls. This work provides an opportunity for the construction of a tunable gap mode as SPR enhancer in a total internal reflection architecture. The systematic study on the relationship between gap modes and SPR sensitivity provides a broad scope for promoting direct, efficient, highly selective, and sensitive detection of SPR sensors for clinical application.

Perspectives and trends in advanced optical and electrochemical biosensors based on engineered peptides.

With the advancement of life medicine, in vitro diagnostics (IVD) technology has become an auxiliary tool for early diagnosis of diseases. However, biosensors for IVD now face some disadvantages such as poor targeting, significant antifouling properties, low density of recognized molecules, and poor stability. In recent years, peptides have been demonstrated to have various functions in unnatural biological systems, such as targeting properties, antifouling properties, and self-assembly properties, which indicates that peptides can be engineered. These properties of peptides, combined with their good biocompatibility, can be well applied to the design of biosensors to solve the problems mentioned above. This review provides an overview of the properties of engineered functional peptides and their applications in enhancing biosensor performance, mainly in the field of optics and electrochemistry.

Aptamer-Assisted Protein Orientation on Silver Magnetic Nanoparticles: Application to Sensitive Leukocyte Cell-Derived Chemotaxin 2 Surface Plasmon Resonance Sensors.

Leukocyte cell-derived chemotaxin 2 (LECT2) has been proved to be a potential biomarker for the diagnosis of liver fibrosis. In this work, a sensitive surface plasmon resonance (SPR) assay for LECT2 analysis was developed. Tyrosine kinase with immune globulin-like and epidermal growth factor-like domains 1 (Tie1) is an orphan receptor of LECT2 with a C-terminal Fc tag, which is far away from the LECT2 binding sites. The Fc aptamer was intentionally used to capture the Tie1 through its Fc tag, connecting with Fe3O4-coated silver magnetic nanoparticles (Ag@MNPs) and ensuring the LECT2 binding site to be outward. Attributed to the orientation nature of the captured protein, Ag@MNPs were able to enhance the SPR signal. A sensitive LECT2 sensor was successfully fabricated with a detection limit of 10.93 pg/mL. The results showed that the immobilization method improved the binding efficiency of Tie1 protein. This strategy could be extended to attach antibodies or recombinant Fc label proteins to Fc aptamer-based nanoparticles.

Antibacterial Activity of Graphene-Based Nanomaterials.

Recent research has shown that graphene as a novel "green" antibacterial material possess excellent antibacterial properties with no risk of bacterial resistance for daily life due to its physical damage-based bactericidal mechanism. Therefore, an increasing amount of research has been focused towards evaluating the antibacterial effects of graphene and graphene-based hybrid materials. In this chapter, we reviewed the antibacterial activity and mechanism of graphene-based nanomaterials and highlighted the importance of size, morphology, and composites in the application of antibacterial materials development. Finally, we made a summary and outlook on this research field.

Inorganic and Metal-Organic Nanocomposites for Cascade-Responsive Imaging and Photochemical Synergistic Effects.

Porphyrins coordinated with platinum(II) chemotherapeutic drugs are attractive for the development of photosensitizers for photodynamic therapy (PDT) of cancer. In this paper, inorganic and metal-organic nanocomposites were synthesized with cascade-responsive imaging and photochemical synergistic effects. After endo/lysosomal escape, the outer metal-organic frameworks were degraded, leading to the release of an excellent photosensitizer (tetrapyridylporphyrin, PtTPyP). Subsequently, doxorubicin (DOX), inserted in the adenosine triphosphate (ATP) aptamer-functionalized gold nanoparticles, was released under the stimulation of endogenous ATP, synergistically enhancing cancer treatment. Fluorescence imaging allowed tracking of PtTPyP and DOX for real-time detection and on-demand therapy. This strategy endowed the nanocomposites with stability, responsiveness, effectiveness, and ease of synthesis, namely, sTREE strategy. Accordingly, our demonstration provided a promising and smart nanocarrier for imaging and drug delivery.

Pyridinium porphyrins and AuNPs mediated bionetworks as SPR signal amplification tags for the ultrasensitive assay of brain natriuretic peptide.

Extension of the self-assembled bionanonetworks into surface plasmon resonance (SPR) assay investigation provides an effective signal amplification approach. We fabricated a bionetwork by nucleic acids, organic compounds, and supramolecular gold nanoparticles for ultrasensitive SPR detection of B-type natriuretic peptide (BNP). The SPR method was developed by a sandwich-type format of aptamer-target-antibody, and the aptamer-modified bionanonetworks induced localized SPR and large refractive index for different concentrations of the target BNP. The linear concentration range and limit of detection were 1-10,000 pg/mL (R2 = 0.9852) and 0.3 pg/mL respectively. The detection recovery was in the range 92.13 to 108.69%. The approach embraces the following main advantages: (1) Cooperative double recognition was realized by calix[4]arenes for amino aptamers and pyridinium porphyrins. (2) The approach provided the specificity for supramolecular-based nanomaterials and a simple synthesis process via the ordered self-assembly under mild conditions. (3) The bionanonetworks endowed the SPR assay with signal amplification and stable determination for trace proteins. Therefore, it is expected that this study may offer a new SPR signal-amplified platform of organic-inorganic bionanonetworks to achieve sensitive, stable, and real-time determination. Graphical abstract Schematic of bionanonetwork based on porphyrin-mediated functionalized gold nanoparticles for SPR signal amplification to quantitatively detect BNP.

Evaluation of ß-Amyloid Peptides Fibrillation Induced by Nanomaterials Based on Molecular Dynamics and Surface Plasmon Resonance.

This report investigated the effect of carbon nanomaterials, single-wall carbon nanotube (SWCNT) and graphene oxide, on fibrillation of ß-amyloid 40 (Aß40) based on surface plasmon resonance (SPR) and molecular dynamics (MD). MD simulations are carried out in order to reveal the molecular mechanisms of the interaction between nanomaterials and Aß40. The strong interaction between Aß40 and nanomaterials is related to Van der Waals forces and the Coulomb force, inducing delicate manipulation of the main bonding energy for fibrillation of Aß40. The interaction energy between the Aß peptide and graphene is higher than that of SWCNT. Experimental results show both carbon nanomaterials enhance the appearance of a critical nucleus for nucleation of peptide fibrils. Graphene is more beneficial to assist the nucleation process than SWCNT. Combination of SPR and molecular dynamics could be a high-throughput method to screen protein fibrillation.

High specific detection of osteopontin using a three-dimensional copolymer layer support based on electrochemical impedance spectroscopy.

Tumor marker detection is essential for the therapy efficiency of early stage tumors and the evaluation of disease progression. Osteopontin (OPN) is supposed to be closely related to several kinds of tumors. In the present study, we describe a label-free electrochemical detection of OPN based on a specific reaction between OPN and its relevant antibody. An artificial three-dimensional (3D) scaffold structure consisting of 11-mercaptoundecanoic acid/6-mercapto-1-hexanol, dextran amino and synthetic peptides was designed as a substrate for the immobilization of the antibody. This substrate was characterized using cyclic voltammetry, atomic force microscopy and Fourier transform infrared reflection spectroscopy. Antibody immobilization and OPN detection were conducted using electrochemical impedance spectroscopy (EIS). The low limit of detection was 0.17 nM. The concentration of cancer risk (5.77 nM) can be selectively detected with a high EIS signal. The fabricated 3D OPN sensor is proposed for application in clinical analysis.

Fabrication of calix[4]arene derivative monolayers to control orientation of antibody immobilization.

Three calix[4]arene (Cal-4) derivatives which separately contain ethylester (1), carboxylic acid (2), and crownether (3) at the lower rim with a common reactive thiol at the upper rim were synthesized and constructed to self-assembled monolayers (SAMs) on Au films. After spectroscopic characterization of the monolayers, surface coverage and orientation of antibody immobilized on the Cal-4 derivative SAMs were studied by surface plasmon resonance (SPR) technique. Experimental results revealed that the antibody could be immobilized on the Cal-4 derivatives spontaneously. The orientation of absorbed antibody on the Cal-4 derivative SAMs is related to the SAM's dipole moment. The possible orientations of the antibody immobilized on the Cal-4 derivative 1 SAM are lying-on or side-on, while on the Cal-4 derivative 2 and Cal-4 derivative 3 head-on and end-on respectively. These experimental results demonstrate the surface dipole moment of Cal-4 derivative appears to be an important factor to antibody orientation. Cal-4 derivatives are useful in developing site direct protein chips.

Construction of a sensitive SWCNTs integrated SPR biosensor for detecting PD-L1+ exosomes based on Fe3O4@TiO2 specific enrichment and signal amplification.

Programmed cell death-ligand 1 positive (PD-L1+) exosomes play a crucial role in the realm of cancer diagnosis and treatment. Nevertheless, due to the intricate nature of biological specimens, coupled with the heterogeneity, low refractive index (RI), and scant surface coverage density of exosomes, traditional surface plasmon resonance (SPR) sensors still do not meet clinical detection requirements. This study utilizes the exceptional electrical and optical attributes of single-walled carbon nanotubes (SWCNTs) as the substrate for SPR sensing, thereby markedly enhancing sensitivity. Furthermore, sp2 hybridized SWCNTs have the ability to load specific recognition elements. Additionally, through the coordination interaction of Ti with phosphate groups and the ferromagnetism of Fe3O4, efficient exosomes isolation and enrichment in complex samples are achievable with the aid of an external magnetic field. Owing to the high-quality and high-RI of Fe3O4@TiO2, the response signal experiences amplification, thus further improving the performance of the SPR biosensor. The linear range of the SPR biosensor constructed by this method is 1.0 × 103 to 1.0 × 107 particles/mL, with a limit of detection (LOD) of 31.9 particles/mL. In the analysis of clinical serum samples, cancer patients can be differentiated from healthy individuals with an Area Under Curve (AUC) of 0.9835. This study not only establishes a novel platform for exosomes direct detection but also offers new perspectives for the sensitive detection of other biomarkers.

Fabrication of a protease sensor for caspase-3 activity detection based on surface plasmon resonance.

Diagnosis of apoptosis is essential to the early detection of therapy efficiency and the evaluation of disease progression. Caspase-3 is supposed to be closely related to cellular apoptosis. We describe here a label-free surface plasmon resonance (SPR) detection of apoptosis based on caspase-3 activity assay through enzyme digestion. An artificial peptide sequence was designed as a substrate of caspase-3 and immobilized on a gold disk through covalent binding. The 4Lys part at the end of the pentadecyl-peptide was designed to form a unique peptide array through electrostatic repulsion. The immobilization of the peptide on the gold surface was carefully characterized by SPR and atomic force microscopy. The catalytic conditions of caspase-3 were optimized with electrochemical impedance spectroscopy. The detection limit of caspase-3 was found at a concentration of 1 pg mL(-1). The activity of caspase-3 in apoptotic cells could also be measured sensitively by the one-step and intuitional SPR response decrease. The fabricated simple and convenient caspase-3 sensor is proposed for application in clinical analysis.

Ti3C2Tx MXene -facilitated non-selective trapping effect: Efficient SERS detection of exosomal PD-L1.

Biosensors developed through a sandwich approach have demonstrated favorable detection performance for exosomal programmed cell death 1 ligand 1 (ExoPD-L1) detection. However, the reported PD-L1 antibodies, peptides, and aptamers utilized in these biosensors typically bind to the extracellular region, with overlapping binding sites that severely constrain the fabrication of biosensors. In this study, we present a simple approach to specifically identify and analyze ExoPD-L1 through the non-selective trapping effect of Ti3C2TX (X=-O, -F, -OH) MXene on exosomes via the formation of Ti-O-P complexation, and the selective capture of peptide-functionalized Au@MPBA (4-Mercaptophenylboronic acid) @SiO2 surface enhanced Raman scattering (SERS) tags on ExoPD-L1. The biosensor delivered a both hypersensitive and reliable performance in exosome detection with a low limit of detection (20.74 particles/mL) in the linear range of 102 to 5×106 particles/mL. Furthermore, the biosensor demonstrated excellent stability and interference resistance in detecting ExoPD-L1 in clinical serum samples, enabling the easy differentiation of breast cancer patients from healthy controls. This work provides new insights into the design of biosensors for exosome detection and can serve as a replicable template for sandwich immunoassay detection for other types of sensors, including but not limited to SERS.

2D MOF-enhanced SPR sensing platform: Facile and ultrasensitive detection of Sulfamethazine via supramolecular probe.

Sulfamethazine (SMZ) is widely present in the environment and can cause severe allergic reactions and cancer in humans. Accurate and facile monitoring of SMZ is crucial for maintaining environmental safety, ecological balance, and human health. In this work, a real-time and label-free surface plasmon resonance (SPR) sensor was devised using a two-dimensional metal-organic framework with superior photoelectric performance as an SPR sensitizer. The supramolecular probe was incorporated at the sensing interface, allowing for the specific capture of SMZ from other analogous antibiotics through host-guest recognition. The intrinsic mechanism of the specific interaction of the supramolecular probe-SMZ was elucidated through the SPR selectivity test in combination with analysis by density functional theory, including p-π conjugation, size effect, electrostatic interaction, π-π stacking, and hydrophobic interaction. This method facilitates a facile and ultrasensitive detection of SMZ with a limit of detection of 75.54 pM. The accurate detection of SMZ in six environmental samples demonstrates the potential practical application of the sensor. Leveraging the specific recognition of supramolecular probes, this direct and simple approach offers a novel pathway for the development of novel SPR biosensors with outstanding sensitivity.

Current methods and emerging approaches for detection of programmed death ligand 1.

Various tumor cells overexpress programmed death ligand 1 (PD-L1), a main immune checkpoint protein (ICP) embedded in the tumor cells membrane, to evade immune recognition through the interaction between PD-L1 and its receptor programmed death 1 (PD-1) which is from T-cells for maintaining immune tolerance. So inhibitors targeting the PD-1 or PD-L1 can block the PD-1/PD-L1 signaling pathway to restore the recognition activity of the immune system to tumor cells, which also have been utilized as a novel approach to improve the clinical therapeutic effect for cancer patients. Since not all cancer patients can respond to these inhibitors effectively, previous diagnosis of PD-L1 is significant to target the right treatments for cancer patients. This review pays attention to the PD-L1 detection and recent progress in the measurement of PD-L1 concentration, including various detection methods based on optical sensors as well as electrochemical assays. Apart from above those, we also focus on the prospects of PD-L1 detection in precision medicine.

Rapid and sensitive detection of PD-L1 exosomes using Cu-TCPP 2D MOF as a SPR sensitizer.

Two-dimensional metal organic framework (2D MOF Cu-TCPP) with significantly enhanced photoelectric properties was synthesized by a simple hydrothermal method. The π-stacked electroactive porphyrin molecules of TCPP-based 2D MOF carry out charge transport in the MOF structure. The d-d band transition of Cu2+ and its 2D ultra-thin characteristics can produce excellent near-infrared light absorption to couple with SPR. Three key parameters including the refractive index sensitivity, detection accuracy and quality factor were improved significantly for 2D MOF modified gold chips. Especially, the refractive index sensitivity was increased from 98 to 137.67°/RIU after modified with 2D MOF. Thus, for the first time, we applied it as a signal enhancer to improve direct SPR assay for the Programmed death ligand-1 (PD-L1) exosomes. Owning to its large specific surface area, excellent photoelectric properties, highly ordered structure, good dispersion and biocompatibility, the LOD of the SPR sensor was 16.7 particles/mL. The reliability and practicability were further validated by analysis of PD-L1 exosomes in human serum samples. The recovery rate was 93.43 %-102.35%, with RSD of 5.79 %-14.6%. Given their excellent signal amplification ability, 2D MOF Cu-TCPP could serve as an ideal SPR sensitizer for rapid and sensitive detection of trace disease markers.

Molecular recognition of arginine by supramolecular complexation with calixarene crown ether based on surface plasmon resonance.

Arginine plays an important role in cell division and the functioning of the immune system. We describe a novel method by which arginine can be identified using an artificial monolayer based on surface plasmon resonance (SPR). The affinity of arginine binding its recognition molecular was compared to that of lysine. In fabrication of an arginine sensing interface, a calix[4]crown ether monolayer was anchored onto a gold surface and then characterized by Fourier Transform infrared reflection absorption spectroscopy, atomic force microscopy, and cyclic voltammetry. The interaction between arginine and its host compound was investigated by SPR. The calix[4]crown ether was found to assemble as a monolayer on the gold surface. Recognition of calix[4]crown monolayer was assessed by the selective binding of arginine. Modification of the SPR chip with the calix[4]crown monolayer provides a reliable and simple experimental platform for investigation of arginine under aqueous conditions.

The magnetic-nanoparticle-assisted sensitive detection of nitrated α-syn in blood based on a sensitizing electrochemical layer.

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease. Nitrated α-synuclein (α-syn) in the blood is a potentially efficient biomarker for PD in its early stages. In this work, an ultrasensitive electrochemical immunosensor was developed for the specific detection of nitrated α-syn. Supramolecule-mediated AuNP composites (GNCs) were modified on the gold electrode as a sensing film to capture anti-nitrated α-syn. Basic characterization studies revealed that GNCs were composed of abundant binding sites and had high conductivity with a large surface area, biocompatibility, and remarkable electrochemical activity. Anti-α-syn-modified magnetic nanoparticles (MNPs) were used as signal amplification tags to construct a sensitive sandwich assay. With a high specific surface area, strong conductivity, and abundant active sites, GNCs as an amplifying matrix can enhance the performance of the immunoassay and obtain preliminary signal amplification. MNPs showed excellent stability and led to a net decrease in the charge-transfer resistance due to their unique spherical structure and high conductivity, resulting in a sensitive electrochemical signal change according to the nitrated α-syn concentration in the sample. Therefore, this simple nitrated α-syn immunoassay with sensitivity and selectivity has potential for practical clinical applications.

Development and evaluation of oligonucleotide chip based on the 16S-23S rRNA gene spacer region for detection of pathogenic microorganisms associated with sepsis.

Oligonucleotide chips targeting the bacterial internal transcribed spacer region (ITS) of the 16S-23S rRNA gene, which contains genus- and species-specific regions, were developed and evaluated. Forty-three sequences were designed consisting of 1 universal, 3 Gram stain-specific, 9 genus-specific, and 30 species-specific probes. The specificity of the probes was confirmed using bacterial type strains including 54 of 52 species belonging to 18 genera. The performance of the probes was evaluated using 825 consecutive samples that were positive by blood culture in broth medium. Among the 825 clinical specimens, 708 (85.8%) were identified correctly by the oligonucleotide chip. Most (536 isolates, or 75.7%) were identified as staphylococci, Escherichia coli, or Klebsiella pneumoniae. Thirty-seven isolates (4.5%) did not bind to the corresponding specific probes. Most of these also were staphylococci, E. coli, or K. pneumoniae and accounted for 6.3% of total number of the species. Sixty-two specimens (7.5%) did not bind the genus- or species-specific probes because of lack of corresponding specific probes. Among them, Acinetobacter baumannii was the single most frequent isolate (26/62). The oligonucleotide chip was highly specific and sensitive in detecting the causative agents of bacteremia directly from positive blood cultures.

Photoluminescence up-conversion of bioconjugated hybrids on CdTe and Au nanoparticles.

Semiconductor nanomaterials have attracted considerable attention in the design of high efficiency PL up-conversion in heterojunctions or nanostructures at extremely low continuous wave (cw)-excitation intensity. In this study, bioconjugated hybrids were constructed using CdTe and Au nanoparticles (NPs), where two-fold PL enhancement was observed in the solution state. These results are in accordance with theoretical predictions of the local-field effects associated with the combined influence of strong localization of the collective plasmon modes in metallic-semiconducting hybrids and multi-photon absorption into its localized plasmon modes. The feasibility of the nanohybrids as sensors was demonstrated by breaking the bioconjugation through thermal stress, which induced a rapid decrease in luminescence intensity. It is believed that the phenomena is applicable to high-compacted optoelectronic devices and sensing systems that take advantage of both quantum confinement effects and nonlinear optical properties.