LabelFree Impedimetric Immunosensors Modulated by Protein ABovine Serum Albumin Layer for Ultrasensitive Detection of Salbutamol The sensing properties of immunosensors are determined not only by the amount of immobilized antibodies but also by the number of effective antigenbinding sites of the immobilized antibody. Protein A (PA) exhibits a high degree of affinity with the Fc part of IgG antibody to feasibly produce oriented antibody immobilization. This work proposes a simple method to control the PA surface density on gold nanostructure (AuNS)deposited screenprinted carbon electrodes (SPCEs) by mixing concentrationvaried PA and bovine serum albumin (BSA), and to explore the effect of PA density on the affinity attachment of antisalbutamol (SAL) antibodies by electrochemical impedance spectroscopy. A concentration of 100 xcexbcgmL PA and 100 xcexbcgmL BSA can obtain a saturated coverage on the 3mercaptoproponic acid (MPA)AuNSSPCEs and exhibit a 50% PA density to adsorb the amount of antiSAL, more than other concentrationvaried PABSAmodified electrodes. Compared with the randomly immobilized antiSALMPAAuNSSPCEs and the antiSALPA(100 xcexbcgmL):BSA(0 xcexbcgmL)MPAAuNSSPCE, the antiSALPA(100 xcexbcgmL): BSA(100 xcexbcgmL)MPAAuNSSPCEbased immunosensors have better sensing properties for SAL detection, with an extremely low detection limit of 0.2 fgmL and high reproducibility (u003c2.5% relative standard deviation). The mixture of PA(100 xcexbcgmL):BSA(100 xcexbcgmL) for the modification of AuNSSPCEs has great promise for forming an optimal protein layer for the oriented adsorption of IgG antibodies to construct ultrasensitive SAL immunosensors.

An Electrochemical Immunosensor Based on a SelfAssembled Monolayer Modified Electrode for LabelFree Detection of xcexb1Synuclein This research demonstrated the development of a simple, costeffective, and labelfree immunosensor for the detection of xcexb1synuclein (xcexb1Syn) based on a cystamine (CYS) selfassembled monolayer (SAM) decorated fluorinedoped tin oxide (FTO) electrode. CYSSAM was formed onto the FTO electrode by the adsorption of CYS molecules through the head sulfur groups. The free amine (xe2x80x93NH2) groups at the tail of the CYSSAM enabled the immobilization of antixcexb1Synantibody, which concurrently allowed the formation of immunocomplex by covalent bonding with xcexb1Synantigen. The variation of the concentrations of the attached xcexb1Syn at the immunosensor probe induced the alternation of the current and the charge transfer resistance (Rct) for the redox response of Fe(CN)63xe2x88x924xe2x88x92, which displayed a linear dynamic range from 10 to 1000 ngmL with a low detection limit (SN  3) of ca. 3.62 and 1.13 ngmL in differential pulse voltammetry (DPV) and electrochemical impedance spectra (EIS) measurements, respectively. The immunosensor displayed good reproducibility, antiinterference ability, and good recoveries of xcexb1Syn detection in diluted human serum samples. The proposed immunosensor is a promising platform to detect xcexb1Syn for the early diagnose of Parkinsonxe2x80x99s disease, which can be extended for the determination of other biologically important biomarkers.