An "in-electrode"-type immunosensing strategy for the detection of squamous cell carcinoma antigen based on electrochemiluminescent AuNPs/g-C3N4 nanocomposites.

A novel "in-electrode"-type electrochemiluminescence (ECL) immunosensor for the sensitive detection of squamous cell carcinoma antigen (SCCA) was constructed using magnetic graphene oxide (nanoFe3O4@GO) and Au nanoparticles/graphitic-phase carbon nitride (AuNPs/g-C3N4). The capture probe was prepared by immobilizing the primary antibody of SCCA (Ab1) on the nanoFe3O4@GO, while the AuNPs/g-C3N4 nanocomposites labelled the secondary antibody of SCCA (Ab2), which acted as a signal tag. The recognition scaffold was the following: the capture probe was immobilized onto the magnetic electrode surface that caught the target SCCA and finally allowed the immobilization of the signal tag via the interaction between antigen and antibody. Importantly, a high ECL signal could be obtained due to the unique immunocomplex, which ensured all of the g-C3N4 on the outmost plane were directly fixed onto the electrode surface and became part of the electrode surface. This resulted in an enhanced efficiency of the g-C3N4 for electrochemical luminescence, thus extending the outer Helmholtz plane (OHP) of the proposed electrode and leading to high sensitivity. Taking advantage of both nanoFe3O4@GO and AuNPs/g-C3N4, the ECL intensity was found to increase logarithmically with SCCA concentration in a wide linear range from 0.001 to 10ng/mL and with a detection limit of 0.4pg/mL. The proposed "in-electrode"-type ECL immunosensor was used to analyse SCCA in human serum, and satisfactory recoveries were obtained, indicating that the proposed method was promising for practical applications in the clinical diagnosis of SCCA.

Faraday cage-type electrochemiluminescence immunosensor for ultrasensitive detection of Vibrio vulnificus based on multi-functionalized graphene oxide.

A novel Faraday cage-type electrochemiluminescence (ECL) immunosensor devoted to the detection of Vibrio vulnificus (VV) was fabricated. The sensing strategy was presented by a unique Faraday cage-type immunocomplex based on immunomagnetic beads (IMBs) and multi-functionalized graphene oxide (GO) labeled with (2,2'-bipyridine)(5-aminophenanthroline)ruthenium (Ru-NH2). The multi-functionalized GO could sit on the electrode surface directly due to the large surface area, abundant functional groups, and good electronic transport property. It ensures that more Ru-NH2 is entirely caged and become "effective," thus improving sensitivity significantly, which resembles extending the outer Helmholtz plane (OHP) of the electrode. Under optimal conditions, the developed immunosensor achieves a limit of detection as low as 1 CFU/mL. Additionally, the proposed immunosensor with high sensitivity and selectivity can be used for the detection of real samples. The novel Faraday cage-type method has shown potential application for the diagnosis of VV and opens up a new avenue in ECL immunoassay. Graphical abstract Faraday cage-type immunoassay mode for ultrasensitive detection by extending OHP.

In-electrode vs. on-electrode: ultrasensitive Faraday cage-type electrochemiluminescence immunoassay.

A new-concept of an "in-electrode" Faraday cage-type electrochemiluminescence immunoassay (ECLIA) method for the ultrasensitive detection of neurotensin (NT) was reported with capture antibody (Ab1)-nanoFe3O4@graphene (GO) and detector antibody (Ab2)&N-(4-aminobutyl)-N-ethylisoluminol (ABEI)@GO, which led to about 1000-fold improvement in sensitivity by extending the Helmholtz plane (OHP) of the proposed electrode assembly effectively.

A label-free multi-functionalized graphene oxide based electrochemiluminscence immunosensor for ultrasensitive and rapid detection of Vibrio parahaemolyticus in seawater and seafood.

A label-free electrochemiluminescence (ECL) immunosensor for ultrasensitive and rapid detection of marine pathogenic bacterium Vibrio parahaemolyticus (VP) in seawater and seafood was developed based on multi-functionalized graphene oxide, which was prepared with N-(4-aminobutyl)-N-ethylisoluminol (ABEI) and VP antibody (anti-VP) simultaneously immobilized on the surface of magnetic graphene oxide (nanoFe3O4@GO). ABEI and anti-VP acted as the electrochemiluminophore and the capture device for VP respectively. Good conductivity and two-dimensional structure of the nanoFe3O4@GO enabled all the ABEI, immobilized on GO, electrochemically active and thus improved the detection sensitivity. Under optimal conditions, the ECL intensity decreased with increasing logarithmic concentrations of VP in the range of 10-10(8)CFU/mL, with a detection limit of 5CFU/mL for seawater and 5CFU/g for seafood. This ECL immunosensor showed high specificity, stability and reproducibility for the detection of VP. In addition, the ECL immunosensor has been successfully used to determine the concentration of VP in seawater and seafood rapidly, with a recovery of 94.4-112.0% and RSD 4.1-11.7%. Therefore, the developed immunosensor shows great prospect for practical application.

A one-step electrochemiluminescence immunosensor preparation for ultrasensitive detection of carbohydrate antigen 19-9 based on multi-functionalized graphene oxide.

A one-step electrochemiluminescence (ECL) immunosensor for ultrasensitive detection of carbohydrate antigen 19-9 (CA19-9) was developed based on multi-functionalized graphene oxide (GO), which was prepared with N-(4-aminobutyl)-N-ethylisoluminol (ABEI) and CA19-9 antibody (anti-CA19-9) chemically bound to the surface of magnetic GO (nanoFe3O4@GO). ABEI and anti-CA19-9 acted as the electrochemiluminophore and the capture device for CA19-9 respectively. NanoFe3O4@GO enabled all the ABEI immobilized molecules electrochemically active due to its good conductivity, and brought multi-functionalized GO attracted on the surface of magnetic glass carbon electrode through magnetism. Thus the ECL immunosensor could be prepared through a one-step process that facilitates ultrasensitive detection of CA19-9. Under optimal conditions, the ECL intensity of the immunosensor decreased proportionally to the logarithmic concentrations of CA19-9 in the range of 0.001-5U/mL with a detection limit of 0.0005U/mL. This one-step ECL immunosensor showed good performance in specificity, stability, reproducibility, regeneration and application. It opened a new avenue to apply multi-functionalized bionanomaterials in ECL immunoassay.

Electrochemiluminescence immunosensor for tumor markers based on biological barcode mode with conductive nanospheres.

A novel sandwich-type electrochemiluminescence (ECL) immunosensor was developed for highly sensitive and selective determination of tumor markers based on biological barcode mode. N-(4-aminobutyl)-N-ethylisoluminol (ABEI) and the second antibody (Ab2) were simultaneously immobilized on conductive nanospheres to construct ABEI/Ab2-CNSs probes, which could form sandwich immunocomplex by Ab2 and emit ECL signals by ABEI. The gold layer coated on the surface of the conductive nanospheres could extend the outer Helmholtz plane (OHP) of the ECL immunosensor effectively. Benefited from it, all ABEI molecules immobilized on conductive nanospheres would act as biological barcode to give in-situ ECL signals without interfering with the activity of the second antibody. In such a case, the sensitivity of the ECL immunosensor would be greatly improved because an antigen molecule would correspond to ECL signals of thousands of ABEI molecules. Using prostate specific antigen (PSA) as a model tumor marker, the ECL intensity was found to increase with the logarithm of PSA concentration with a wide linear range from 0.04 to 10 fg/mL. In addition, specificity, stability, reproducibility, regeneration and application were satisfactory. Therefore, this developed ECL immunosensor has a potential for practical detection of disease-related proteins besides tumor markers in the clinical diagnostics.