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 À1 . 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.

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.

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