Electrochemical determination of caspase-3 using signal amplification by HeLa cells modified with silver nanoparticles.

An electrochemical sensor capable of quantitative determination of caspase-3 activities was developed. A thiolated peptide whose sequence contained a caspase-3 cleaved site and a cell penetration sequence was preimmobilized onto an electrode. The quantification of caspase-3 was accomplished after cell penetration and the subsequent adsorption of silver nanoparticles (AgNPs). The oxidation current of AgNPs was found to be inversely proportional to the concentration of caspase-3 between 0.02 and 0.2 U/mL. A detection limit of 0.02 U/mL for caspase-3 was achieved due to the large number of positively charged AgNPs adsorbed onto the negatively charged cells. The proof of concept was demonstrated by monitoring the cleavage of surface-confined peptide substrates by caspase-3 in cell lysates. The current sensor could be extended to detect cells by replacing the surface-confined peptide with aptamers that recognize cells. Thus, the use of a cell as a matrix for AgNPs shows excellent potential for constructing electrochemical sensors and provides a useful alternative for sensor development in the future. Cells modified with silver nanoparticles were utilized as the electrochemical readout of an electrochemical assay.

Toehold-Mediated Strand Displacement Reaction for Dual-Signal Electrochemical Assay of Apolipoprotein E Genotyping.

Apolipoprotein E (apoE) polymorphic genes are one of the main genetic determinants of Alzheimer's disease (AD) risk. Relying on the toehold-mediated strand displacement reaction (SDR), the dual-signal electrochemical assay of apoE genotyping with potential applications in the early diagnosis of AD has been achieved. The displacement of the surface-confined methylene blue- and ferrocene-capped detection probe-modified gold nanoparticles (AuNPs) by the complementary sequences (Tc 1 and Tc 2, fragment of allele ε4 at codon 112 and that of allele ε3 or ε4 at codon 158, respectively), triggered by the highly specific SDR, results in decreased voltammetric signals. In contrast, partial strand displacement caused by the single mismatched sequences (Tsm 1 and Tsm 2, fragment of allele ε2 or ε3 at codon 112 and that of allele ε2 at codon 158, respectively) produces larger voltammetric signals. The proposed method serves as a versatile platform for the discrimination of six apoE genotypes, including three homozygotes (ε2/2, ε3/3, and ε4/4) and three heterozygotes (ε2/3, ε2/4, and ε3/4), and for the quantification of apoE ε3/3 from genomic DNA extracts of AD patients.

NIR Light-Responsive Hollow Porous Gold Nanospheres for Controllable Pressure-Based Sensing and Photothermal Therapy of Cancer Cells.

Pressure-based signal transduction has attracted recent and extensive attention due to its high sensitivity and simplicity. The most popular way to generate gas pressure relies on catalyst-mediated decomposition of H2O2. Despite its high sensitivity, this method lacks spatial and temporal control of the reaction, and may suffer from variations due to the dead time of mixing. In this work, we report a new reaction using near-infrared (NIR) light to heat hollow porous gold nanospheres (AuNSs) for thermal decomposition of NH4HCO3. Comparisons were made on these two systems especially on controlled pressure production. As an example of application, our light-controlled system was used for the detection of MCF-7 cancer cells by attaching the S2.2 aptamer on the AuNSs. The detection limit was as low as 2 cells/mL. Meanwhile, the heat produced by the AuNSs was used to induce localized hyperthermia at the surface of the cancer cells. This interesting theranostic system provides new insights into pressure-based sensing and may inspire new analytical applications.