Femto-molar detection of cancer marker-protein based on immuno-nanoplasmonics at single-nanoparticle scale

Recent Development of Nanomaterials-Based Cytosensors for the Detection of Circulating Tumor Cells

The accurate analysis of circulating tumor cells (CTCs) holds great promise in early diagnosis and prognosis of cancers. However, the extremely low abundance of CTCs in peripheral blood samples limits the practical utility of the traditional methods for CTCs detection. Thus, novel and powerful strategies have been proposed for sensitive detection of CTCs. In particular, nanomaterials with exceptional physical and chemical properties have been used to fabricate cytosensors for amplifying the signal and enhancing the sensitivity. In this review, we summarize the recent development of nanomaterials-based optical and electrochemical analytical techniques for CTCs detection, including fluorescence, colorimetry, surface-enhanced Raman scattering, chemiluminescence, electrochemistry, electrochemiluminescence, photoelectrochemistry and so on.

Multimodal cellular redox nanosensors based on self-doped polyaniline nanocomposites

We have successfully fabricated a nanocomposite, which is composed of polyaniline (PAni) and pyrene butyric acid (Pyba) via a solvent shift method, which was self-doped at a neutral pH value. This PAni nanocomposite can act as a fine nanoagent expressing absorbance, fluorescence, and Raman properties according to the surrounding pH values.

Aptamer based recognition of cancer cells: Recent progress and challenges in bioanalysis

Rapid and accurate monitoring of cancer cells with high sensitivity is essential for a successful cancer treatment. As high-affinity nucleic acid ligands, aptamers can improve the properties of detection methods by conjugating with intracellular or extracellular cancer biomarkers. Despite the advances in the early detection and treatment of cancer cells, lacking effective early detection tools is one of the causes of a high mortality rate. Aptasensors, which are based on the specificity of aptamer-target recognition, with transduction for analytical purposes have received particular attention due to their high sensitivity and selectivity, simple instrumentation, as well as low production cost. In this review, some selective and sensitive methods were summarized based on advanced nanomaterials towards aptasensing of cancer cells, such as blood, breast, cervical, colon, gastric, liver, and lung cancer cells. This review summarizes advances from 2010 to June 2020 in the development of aptasensors for cancer cell detection. Various aptasensing strategies are assessed according to their potential for reaching relevant limits of sensitivity, specificity, and degrees of multiplexing. Furthermore, we address the remaining challenges and opportunities to integrate aptasensing platforms into point-of-care solutions. Finally, the advantages and limitations of aptamer-based aptasensing strategies were reviewed.

Optical and electrochemical-based nano-aptasensing approaches for the detection of circulating tumor cells (CTCs)

More recently, detection of circulating tumor cells (CTCs) has been considered as an appealing prognostic and diagnostic approach for cancer patients. CTCs as a type of tumor-derived cells are secreted by the tumor and released into the blood circulation. Since the migration of CTCs is an early event in cancer progression, patients who still have tumor-free lymph nodes have to be well examined for the CTCs presence in their blood circulation. Nowadays, there is a broad range of detection methods available to identify CTCs. As artificial RNA oligonucleotides or single-stranded DNA with receptor and catalytic characteristics, aptamers have been standing out, owing to their target-induced conformational modifications, elevated stability, and target specificity to be implemented in biosensing techniques. To date, several sensitivity-enhancement methods alongside smart nanomaterials have been used for the creation of new aptasensors to address the limit of detection (LOD), and improve the sensitivity of numerous analyte identification methods. The present review article supports a focused overview of the recent studies in the identification and quantitative determination of CTCs by aptamer-based biosensors and nanobiosensors.

A surface plasmon field-enhanced fluorescence reversible split aptamer biosensor

Surface plasmon field-enhanced fluorescence is reported for the readout of a heterogeneous assay that utilizes low affinity split aptamer ligands. Weak affinity ligands that reversibly interact with target analytes hold potential for facile implementation in continuous monitoring biosensor systems. This functionality is not possible without the regeneration of more commonly used assays relying on high affinity ligands and end-point measurement. In fluorescence-based sensors, the use of low affinity ligands allows avoiding this step but it imposes a challenge associated with the weak optical response to the specific capture of the target analyte which is also often masked by a strong background. The coupling of fluorophore labels with a confined field of surface plasmons is reported for strong amplification of the fluorescence signal emitted from the sensor surface and its efficient discrimination from the background. This optical scheme is demonstrated for time-resolved analysis of chosen model analytes - adenoside and adenosine triphosphate - with a split aptamer that exhibits an equilibrium affinity binding constant between 0.73 and 1.35 mM. The developed biosensor enables rapid and specific discrimination of target analyte concentration changes from low μM to mM in buffer as well as in 10% serum.

Cell-targeting aptamers act as intracellular delivery vehicles

Aptamers are single-stranded nucleic acids or peptides identified from a randomized combinatorial library through specific interaction with the target of interest. Targets can be of any size, from small molecules to whole cells, attesting to the versatility of aptamers for binding a wide range of targets. Aptamers show drug properties that are analogous to antibodies, with high specificity and affinity to their target molecules. Aptamers can penetrate disease-causing microbial and mammalian cells. Generated aptamers that target surface biomarkers act as cell-targeting agents and intracellular delivery vehicles. Within this context, the "cell-internalizing aptamers" are widely investigated via the process of cell uptake with selective binding during in vivo systematic evolution of ligands by exponential enrichment (SELEX) or by cell-internalization SELEX, which targets cell surface antigens to be receptors. These internalizing aptamers are highly preferable for the localization and functional analyses of multiple targets. In this overview, we discuss the ways by which internalizing aptamers are generated and their successful applications. Furthermore, theranostic approaches featuring cell-internalized aptamers are discussed with the purpose of analyzing and diagnosing disease-causing pathogens.