Aptasensor based on triplex switch for SERS detection of cytochrome c

Cytochrome c in cancer therapy and prognosis

Cytochrome c (cyt c) is an electron transporter of the mitochondrial respiratory chain. Upon permeabilization of the mitochondrial outer membrane, cyt c is released into the cytoplasm, where it triggers the intrinsic pathway of apoptosis. Cytoplasmic cyt c can further reach the bloodstream. Apoptosis inhibition is one of the hallmarks of cancer and its induction in tumors is a widely used therapeutic approach. Apoptosis inhibition and induction correlate with decreased and increased serum levels of cyt c, respectively. The quantification of cyt c in the serum is useful in the monitoring of patient response to chemotherapy, with potential prognosis value. Several highly sensitive biosensors have been developed for the quantification of cyt c levels in human serum. Moreover, the delivery of exogenous cyt c to the cytoplasm of cancer cells is an effective approach for inducing their apoptosis. Similarly, several protein-based and nanoparticle-based systems have been developed for the therapeutic delivery of cyt c to cancer cells. As such, cyt c is a human protein with promising value in cancer prognosis and therapy. In addition, its thermal stability can be extended through PEGylation and ionic liquid storage. These processes could contribute to enhancing its therapeutic exploitation in clinical facilities with limited refrigeration conditions. Here, I discuss these research lines and how their timely conjunction can advance cancer therapy and prognosis.

Applications of triplex DNA nanostructures in sensor development

Triplex DNA nanostructures are one of the most emerging and fascinating self-assembled nanostructures due to their unique nanoparticle-like organization and inherit characteristics. They have attracted numerous interests recently because of their versatile and powerful utility in diverse areas of science and technology, such as clinical or disease diagnosis and stimuli-based drug delivery. This review addresses particularly the utilization of DNA triplexes in the development of biosensors for detecting nucleic acid; strategies in sensing pH, protein activity, ions, or molecules. Finally, an outlook for potential applications of triplex DNA nanoswitches is provided.

Fabrication of large size individual octahedral tungsten oxide hydrate and Au NPs as SERS platforms for sensitive detection of cytochrome C

Surface-enhanced Raman scattering (SERS) has attracted much attention with its powerful trace detection and analysis capabilities, especially biological and environmental molecules. However, building a protein SERS detection platform based on semiconductor devices is a huge challenge. Herein, through the synergy of NH₃ and nickel foam, a large-sized semiconductor tungsten oxide hydrate platform (WOHP) was synthesized. The crystal plane of a single WOHP particle is larger than the excitation spot. As a SERS substrate, WOHP can make full use of the excitation light without destroying the structure during the protein molecules detection process. Through the synergy of WOHP and Au NPs, the enhancement factor is 1.5 × 10⁴. Raman peaks of WOHP can be used as references for the detection of typical protein cytochrome C (Cyt C). As the Cyt C concentration decreases, the I_{Cyt C}/I_WOHP ratio decreases, and the signal can still be obtained when the concentration is as low as 5 × 10^-9 mol L^-1. More importantly, the method does not affect the catalytic activity of Cyt C and can be applied to the detection of Cyt C concentration in serum.

Gold-Nanoparticle-Functionalized Cobalt-Nickel Phosphate 3D Nanoice Creams to Fabricate Stable and Sensitive Biosensors for the Cytochrome c Assay

Designing a stable and sensitive luminol-based electrochemiluminescence (ECL) analytical platform in the neutral condition has attracted a lot of attention. Here, gold-nanoparticle-functionalized cobalt-nickel phosphate three-dimensional nanoice creams (Au@Co₃Ni₃(PO₄)₄ NICs) are successfully prepared via electrostatic interaction. Generally, cobalt-nickel phosphate nanoice creams (Co₃Ni₃(PO₄)₄ NICs) are synthesized via a mild hydrothermal method and functionalized via polyethylenimine (PEI). Then, Au NPs are adsorbed on the surface of Co₃Ni₃(PO₄)₄ NICs via Au-N weak interaction to fabricate Au@Co₃Ni₃(PO₄)₄ NICs. Owing to the important roles of Au@Co₃Ni₃(PO₄)₄ in exhibiting excellent electrocatalytic activity, as well as preventing the deposition of negatively charged oxidation product induced electrode passivation, luminol in the nanohybrids (LH-Au@Co₃Ni₃(PO₄)₄) gives strong and stable ECL intensity in the neutral conditions. Moreover, the ECL emission of luminol is obviously quenched based on the resonance energy transfer (RET) between luminol as donor and cytochrome c (Cyt c) as acceptor. Hence, a sensitive ECL biosensor is successfully fabricated for the quantitative determination of Cyt c in cell lysates and exhibits wide linear ranges of 1.0 × 10^-4-0.5 × 10^-5 and 0.5 × 10^-5-1.0 × 10^-8 M as well as a low detection limit of 2.48 nM. This novel sensing strategy will broaden the application of transition metal (Co, Ni) phosphates in bioassays.

Highly sensitive IRS based biosensor for the determination of cytochrome c as a cancer marker by using nanoporous anodic alumina modified with trypsin

The determination of cytochrome c in the human serum sample is a regular medical investigation performed to assess cancer diseases. Herein, we used interferometric reflectance spectroscopy (IRS) based biosensor for the determination of cytochrome c. For this purpose first, the nanoporous anodic alumina (NAA) was fabricated. Then, the NAA pore walls were functionalized with 3-aminopropyl trimethoxy silane (NAA-NH₂). Subsequently, the trypsin enzyme was immobilized on the NAA pore walls. The sensing principle of proposed IRS sensor to cytochrome c is based on a change in the intensity of the reflected light to a charge-coupled device (CCD) detector after digesting of cytochrome c by immobilized trypsin enzymes on NAA-NH₂ into the heme-peptide fragment. The heme-peptide fragment then oxidized 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) to green color ABTS^·- anion radical in the presence of hydrogen peroxide. The generated green color ABTS^·- anion radical solution adsorbed the white light and therefore the intensity of the reflected light from NAA to the CCD decreased. The decrease in the intensity of the white light had a logarithmic relationship with the concentration of the cytochrome c in the range of 1-100 nM. The limit of detections (LOD) for cytochrome c was 0.5 nM. The proposed biosensor exhibited high selectivity, sensitivity, and good stability.

Surface-Enhanced Raman Scattering-Fluorescence Dual-Mode Nanosensors for Quantitative Detection of Cytochrome c in Living Cells

During apoptosis process, the release of cytochrome c (Cyt c) is considered to be a key factor in the intrinsic pathway and is often defined as no regression point. Quantitative detection of intracellular Cyt c remains a challenge. Herein, we have developed surface-enhanced Raman scattering (SERS)-fluorescence dual-mode nanosensors for the quantitative assay of Cyt c in living cells. Dual signal detection was achieved by constructing gold nanotriangles (AuNTs) nanosensors capable of specifically recognizing Cyt c. The nanosensors were prepared by modifying the aptamer of Cyt c on AuNTs and connecting the complementary strands modified with Cy5. The AuNTs provided both enhanced SERS signals and fluorescence quenching effects. Once cells were induced by external stimulus (such as toxins) to release Cyt c, Cyt c would specifically bind to its aptamer, and the complementary strands modified with Cy5 would detach which would result in weakened SERS signal and recovery of fluorescence signal. The experimental results showed that the nanosensors not only had excellent selectivity and sensitivity but also realized real-time monitoring of Cyt c translocation event from mitochondria to cytoplasm. The SERS and fluorescence intensity showed good linear relationship with Cyt c concentration ranging from 0.044 to 9.95 μM and achieved a minimum limit of detection (LOD) of 0.02 μM in living cells. The accuracy of intracellular Cyt c quantitative results was more than 90% compared with the ELISA results.

SERS Quantification and Characterization of Proteins and Other Biomolecules

Changes in protein expression levels and protein structure may indicate genomic mutations and may be related to some diseases. Therefore, the precise quantification and characterization of proteins can be used for disease diagnosis. Compared with several other alternative methods, surface-enhanced Raman scattering (SERS) spectroscopy is regarded as an excellent choice for the quantification and structural characterization of proteins. Herein, we review the main advance of using plasmonic nanostructures as SERS sensing platform for this purpose. Three design approaches, including direct SERS, indirect SERS, and SERS-encoded nanoparticles, are discussed in the direction of developing new precise approaches of quantification and characterization of proteins. While this Review is focused on proteins, in order to highlight concepts of SERS-based sensors also detection of other biomolecules will be discussed.

Recent advances in cytochrome c biosensing technologies

This review is an attempt, for the first time, to describe advancements in sensing technology for cytochrome c (cyt c) detection, at point-of-care (POC) application. Cyt c, a heme containing metalloprotein is located in the intermembrane space of mitochondria and released into bloodstream during pathological conditions. The release of cyt c from mitochondria is a key initiative step in the activation of cell death pathways. Circulating cyt c levels represents a novel in-vivo marker of mitochondrial injury after resuscitation from heart failure and chemotherapy. Thus, cyt c detection is not only serving as an apoptosis biomarker, but also is of great importance to understand certain diseases at cellular level. Various existing techniques such as enzyme-linked immunosorbent assays (ELISA), Western blot, high performance liquid chromatography (HPLC), spectrophotometry and flow cytometry have been used to estimate cyt c. However, the implementation of these techniques at POC application is limited due to longer analysis time, expensive instruments and expertise needed for operation. To overcome these challenges, significant efforts are being made to develop electrochemical biosensing technologies for fast, accurate, selective, and sensitive detection of cyt c. Presented review describes the cutting edge technologies available in the laboratories to detect cyt c. The recent advancements in designing and development of electrochemical cyt c biosensors for the quantification of cyt c are also discussed. This review also highlights the POC cyt c biosensors developed recently, that would prove of interest to biologist and therapist to get real time informatics needed to evaluate death process, diseases progression, therapeutics and processes related with mitochondrial injury.