•A signal-amplification SPR platform was designed to detect small biomolecules.•Calix[4]arene derivative modified AuNP was used as a dual-function reagent.•This strategy is a new concept for the design of highly selective methods.A signal-amplification and dual-recognition strategy was designed to construct a signal-enhanced surface plasmon resonance (SPR) platform for the highly sensitive detection of dopamine. This strategy was based on the specific recognition of boronic acid to diol and that of calix[4]arene crown ether-modified gold nanoparticles (CAL[4]-AuNPs) to amine groups. A 3-aminophenyl boronic acid monohydrate probe was immobilized onto a gold chip surface as capture probes via covalent bonds with 11-mercaptoundecanoic acid. CAL[4]-AuNPs were designed as signal probes and characterized by transmission electron microscopy and spectroscopic techniques. Upon the binding of dopamine with boronic acid followed by CAL[4]-AuNPs, the AuNPs were captured on the chip surface to enhance the SPR signal, thereby producing an ultra-low background signal. Signal amplification and dual recognition were used to quantify dopamine concentration from 0.1 nM to 1 μM, with a detection limit of 1.17 pM. This strategy is a new concept for the design of highly selective analytical methods to detect small biomolecules.

Diamine oxidase (DAO) is involved in regulating ingested or endogenous histamine, several types of human cancer, and the cell mass during embryonic development. Furthermore, DAO is a potential indicator of intestinal mucosa damage in inflammatory and neoplastic diseases or after chemotherapy. Therefore, developing a biosensor is urgently needed to assay DAO activity. In this work, a simple but sensitive colorimetric biosensor is developed for DAO assay and inhibitor screening. The biosensor is based on host-guest interactions between the amine group on the terminal of 1,6-hexanediamine (HMD) and p-sulfonatocalix[6]arene (pSC6). These interactions may aggregate pSC6 modified gold nanoparticles (AuNPs) and induce the corresponding color change of the test solution. Specifically, AuNP aggregation is affected because coordination reactivity does not exist between oxidized HMD and pSC6 during HMD oxidation by DAO. Therefore, a simple colorimetric method with high sensitivity for the assay of DAO activity is proposed. A linear relationship is presented under optimized experimental conditions in a range of 0.15 mU mL−1 to 4.5 mU mL−1 with the lowest detection limit of 0.062 mU mL−1. Moreover, the inhibition effect of guanidine on DAO activity is tested with the IC50 value of 2.4 μM using the proposed biosensor. Therefore, this biosensor has great potential not only for the detection of DAO activity but also for inhibitor screening in future.

The magneto-plamonic nanoparticles (MPNs) have been employed to enhance the signal of surface plasmon resonance (SPR) spectroscopy to gain new insight into MPN and gold film SPR interaction. Three different morphologies MPNs (sphere, short spiky and long spiky) of Fe3O4@Au nanoparticles with good dispersion were synthesized and characterized carefully. A sandwich SPR immunosensor was constructed by immobilizing gold binding anti-CFP-10 (Ab1) onto a gold chip surface via Au-S bond firstly. Gold binding anti-CFP-10 (Ab2) captured on MPN surface was utilized to amplify the SPR signals specifically. Compared with spiky MPNs, the structure of spherical MPN, which concentrates the electric charge density and immobilize more Abs on its surface coverage, could enhance the electronic coupling effect significantly. Attribute to the super paramagnetism of MPNs, a facile solution route was fabricated to capture and separate analyte from the real sample by outside extend magnetic field. Implementation of MPNs results in 30-fold enlargement of the SPR signal at the limit of detection. To this end, an immunoassay is carried out that couples the specificity of antibody-antigen interactions with the high sensitivity based on spherical MPNs signal enhancement SPR.

Peptides, as the simplest biological recognition elements have been developed as probes to capture multitudinous targets. One important factor in fabricating peptide biochips is to immobilize peptides without losing their activity on a solid phase. To keep them functional, it is necessary to immobilize peptide in an oriented way. Calix[4]arene crown ether (CC) has been used as a protein linker molecule on the solid surface. In this study, calix[4]arene crown ether was self-assembled and modified on a gold surface. The calix[4]arene crown ether monolayer was characterized by EIS and SPR. An elaborately designed peptide probe Ac-CCPGCAAAARRRR-NH2 is employed here for the assay of Zn2+. This tridecapeptide consists of a binding part (CCPGC), spacer (AAAA) and immobilization part (RRRR) to interact with a CC SAM. We compared the sensitivity and the specificity of the linker molecules with those of common attachment agents using a zinc ion binding peptide. The fabricated chip showed a superior sensitivity and a much lower detection limit than those chips prepared by other methods. Thus, the calix[4]arene crown ether chip can be used as a powerful peptide linker with a wide range of applications, including peptide–drug interaction, peptide–cell interaction, and an enzyme activity assay.

•The host-guest recognition mediated AuNPs assembly.•SPR signals are improved through the layer-by-layer assembly of AuNPs.•The detection limit of caspase-3 can be achieved as low as 2.2 fg/mL.Cucurbit[7]uril (CB[7]) has received increasing attention because of its unique structure and multiple recognition properties. To improve the sensitivity of surface plasmon resonance (SPR) biosensors, we designed a novel strategy in which caspase-3 serves as the model analyte and CB[7]-modified AuNPs (CB[7]-AuNPs) act as the intermedium. The substrate peptides can be cleaved and replaced with a new N-terminal Phe residue in presence of caspase-3. The CB[7]-AuNPs combine with the N-terminal Phe on the gold chip surface through incorporating the side chain within the nonpolar CB[7] cavity and chelating the N-terminal ammonium group with CB[7] carbonyl oxygen. Then CB[7]-AuNPs integrate with short peptide-modified AuNPs containing Phe at the N-terminal of the peptide. SPR signals are significantly improved through the layer-by-layer assembly of AuNPs. The well-designed sensing platform allows the detection of caspase-3 in a linear range from 10 fg/mL to 103 fg/mL with a detection limit of 2.2 fg/mL. Given its high specificity and desirable sensitivity, this CB[7]-assisted SPR method may be a useful tool for the assay of caspase-3 in the future. This work may also afford a new model to improve the sensitivity and selectivity of SPR biosensors in other protein detection experiments and disease diagnosis.

Accurate diagnosis of breast cancer cells is important on determining the stage of the disease and designing the suitable therapies. Herein, we report a sensitive biosensor based on surface plasmon resonance (SPR) spectroscopy for the detection of breast cancer cells (MCF-7). Firstly, calix[4]arene crownether was used to form a self-assembled monolayer (SAM) on the gold surface. The designed peptide containing recognization and spacer parts was immobilized on the calixarene monolayer surface through host-guest interactions between the ionized amine group of lysine and crown moiety orientedly. The peptide can recognize and capture target breast cancer cells on the surface selectively and sensitively. The detection limit can be achieved as low as 197 cells mL−1. The phenomenon in experiments can be characterized through the intuitional SPR signal increase by the SPR instrument. The fabricated simple and convenient MCF-7 sensor is proposed for application in clinical analysis.

•A facile and versatile method for one-pot synthesis of macrocycle functionalized AuNPs is proposed.•With as-prepared calix[4]arene crown ether (CCE4) functionalized AuNPs, visual host–guest recognition of diamines is carried out successfully.•The sensing of diamines is mediated by the size-selective encapsulation of amine guest into the cavity of the macrocycle host.•This very simple method might also be expanded to other macrocycles for the functionalization of nanomaterials.Since amine compounds have been widespread pollutants in nature and they are extensively used in pharmaceutical industeries and dye manufacturing, it is highly desirable to develop simple, effective and naked-eye available analytical methods for such aliphatic diamines determination. Calixarenes as macrocycles have drawn intensive interests for fields such as biomedicine, supramolecular chemistry and smart materials. Here, instead of the normal complicated modification strategy, a facile and efficient method for one-pot synthesis of calix[4]arene crown ether (CCE4) capped gold nanoparticles (AuNPs) is proposed. The as-prepared CCE4–AuNPs are not only high water dispersity and stability even after storage for 3 months, but also capable of host–guest recognition of diamines in aqueous systems. Size-selective encapsulation of amine group between CCE4 and diamines carry out the aggregation of CCE4–AuNPs. The determination of diamines such as hexamethylenediamine or spermine can be realized by the UV–vis absorbance change and visual color difference.

Today tuberculosis (TB) remains one of the biggest health problems with high rates of morbidity and mortality in the world. An antigen, CFP-10, which found in tissue fluids of tuberculosis patients can be used as the marker protein for early and simplified diagnosis of TB. A sensitive format for immunosorbent assays has been developed to meet the increasing levels of performance demanded in the medical, veterinary, and bioterrorism prevention arenas. This paper introduces the concept of a NiO-decorated SWNTs substrate as a facile means to capture histagged antibody orientedly and increase its surface capacity and thereby improve the detection limit. To this end, histagged anti-CFP-10 was immobilized on a NiO-decorated SWNTs modified substrate via chelation between NiO and histidine-tags. An immuno assay is carried out that couples the specificity of antibody–antigen interactions with the high sensitivity based on surface plasmon resonance detection. The effect of NiO-SWNTs on the orientation of antibody was investigated through comparing with the SWNTs. Implementation of NiO-SWNTs resulted in 22-fold enlargement of the SPR signal at the limit of detection.

Bioactivity of proteins is evaluated to test the adverse effects of nanoparticles interjected into biological systems. Surface plasmon resonance (SPR) spectroscopy detects binding affinity that is normally related to biological activity. Utilizing SPR spectroscopy, a concise testing matrix is established by investigating the adsorption level of bovine serum albumin (BSA) and anti-BSA on the surface covered with 11-mercaptoundecanoic acid (MUA); magnetic nanoparticles (MNPs) and single-walled carbon nanotubes (SWCNTs), respectively. The immunoactivity of BSA on MNPs and SWCNT decreased by 18 % and 5 %, respectively, compared to that on the gold film modified with MUA. This indicates that MNPs cause a considerable loss of biological activity of adsorbed protein. This effect can be utilized for practical applications on detailed biophysical research and nanotoxicity studies.