Recent advances in optical biosensing and imaging of telomerase activity and relevant signal amplification strategies.

Telomerase as a new valuable biomarker for early diagnosis and prognosis evaluation of cancer has attracted much interest in the field of biosensors, cell imaging, and drug screening. In this review, we mainly focus on different optical techniques and various signal amplification strategies for telomerase activity determination. Fluorometric, colorimetry, chemiluminescence, surface-enhanced Raman scattering (SERS), and dual-mode techniques for telomerase sensing and imaging are summarized. Signal amplification strategies include two categories: one is nucleic acid-based amplification, such as rolling circle amplification (RCA), the hybridization chain reaction (HCR), and catalytic hairpin assembly (CHA); the other is nanomaterial-assisted amplification, including metal nanoclusters, quantum dots, transition metal compounds, graphene oxide, and DNA nanomaterials. Challenges and prospects are also discussed to provide new insights for future development of multifunctional strategies and techniques for in situ and in vivo analysis of biomarkers for accurate cancer diagnosis.

Robust nontarget DNA-triggered catalytic hairpin assembly amplification strategy for the improved sensing of microRNA in complex biological matrices.

A simple but robust fluorescence strategy based on a nontarget DNA-triggered catalytic hairpin assembly (CHA) was constructed to probe microRNA-21 (miR-21). A short ssDNA rather than degradable target miRNA was employed as an initiator. Two molecular beacons needed to assist the CHA process were simplified to avoid unfavorable nonspecific interactions. In the presence of the target, the initiator was released from a partially duplex and triggered the cyclic CHA reaction, resulting in a significantly amplified optical readout. A wide linear range from 0.1 pM to 1000 pM for the sensing of miR-21 in buffer was achieved with a low detection limit of 0.76 pM. Fortunately, this strategy demonstrated an obviously improved performance for miR-21 detection in diluted serum. The fluorescence signals were enhanced remarkably and the sensitivity was further improved to 0.12 pM in 10% serum. The stability for miR-21 quantification and the capability for the analysis of single nucleotide polymorphisms (SNPs) were also improved greatly. More importantly, the biosensor could be applied to image miR-21 in different living tumor cells with high resolution, illustrating its promising potential for the assay of miRNAs in various complex situations for early-stage disease diagnosis and biological studies in cells.

Recent Progress of SERS Nanoprobe for pH Detecting and Its Application in Biological Imaging.

As pH value almost affects the function of cells and organisms in all aspects, in biology, biochemical and many other research fields, it is necessary to apply simple, intuitive, sensitive, stable detection of pH and base characteristics inside and outside the cell. Therefore, many research groups have explored the design and application of pH probes based on surface enhanced Raman scattering (SERS). In this review article, we discussed the basic theoretical background of explaining the working mechanism of pH SERS sensors, and also briefly described the significance of cell pH measurement, and simply classified and summarized the factors that affected the performance of pH SERS probes. Some applications of pH probes based on surface enhanced Raman scattering in intracellular and extracellular pH imaging and the combination of other analytical detection techniques are described. Finally, the development prospect of this field is presented.

Hyaluronic Acid Nanoparticles Based on a Conjugated Oligomer Photosensitizer: Target-Specific Two-Photon Imaging, Redox-Sensitive Drug Delivery, and Synergistic Chemo-Photodynamic Therapy.

Self-assembled hyaluronic acid (HA) nanoparticles have been extensively investigated as anticancer therapeutic agents due to the biocompatibility, biodegradability, and active targeting characteristics of HA. However, many HA nanoparticles are restricted to the applications in drug delivery for chemotherapy or lack effective imaging agents. Hence, we developed the camptothecin (CPT)-loaded HA-SS-BFVPBT nanoparticles (HSBNPs) as a multifunctional platform for two-photon imaging and synergistic chemo-photodynamic therapy at the same time. A novel conjugated oligomer photosensitizer, BFVPBT, which was conjugated onto HA through the redox-responsive disulfide linkage (SS), could not only provide a hydrophobic domain for the formation of nanoparticles and drug entrapment but also act as a two-photon photosensitizer that can be directly excited and simultaneously used in two-photon imaging and photodynamic therapy (PDT). HeLa cells overexpressing the HA receptor (CD44) were used for in vitro studies, which proved the specific cellular uptake of CPT-loaded HSBNPs and excellent two-photon PDT/chemotherapy synergistic effect. The nanoparticles have also been shown to realize tumor-targeting in vivo imaging in HeLa-tumor-bearing mice. Moreover, the fluorescence of CPT-loaded HSBNPs could be activated due to the degradation by the reductive glutathione (GSH) and overexpressed hyaluronidases (Hyal-1) in cancer cells, and the intracellular drug release rate was quickened, thus improving the probability of precise cancer diagnosis and therapy. Accordingly, this HSBNPs system is also anticipated to be a precise nanocarrier for other imaging and therapeutic agents besides CPT, offering a promising new avenue for imaging-guided efficient cancer therapy.

On-Electrode Synthesis of Shape-Controlled Hierarchical Flower-Like Gold Nanostructures for Efficient Interfacial DNA Assembly and Sensitive Electrochemical Sensing of MicroRNA.

The performance for biomolecular detection is closely associated with the interfacial structure of a biosensor, which profoundly affects both thermodynamics and kinetics of the assembly, binding and signal transduction of biomolecules. Herein, it is reported on a one-step and template-free on-electrode synthesis method for making shape-controlled gold nanostructures on indium tin oxide substrates, which provide an electrochemical sensing platform for ultrasensitive detection of nucleic acids. Thus-prepared hierarchical flower-like gold nanostructures (HFGNs) possess large surface area that can readily accommodate the assembly of DNA probes for subsequent hybridization detection. It is found that the sensitivity for electrochemical DNA sensing is critically dependent on the morphology of HFGNs. By using this new strategy, a highly sensitive electrochemical biosensor is developed for label-free detection of microRNA-21 (miRNA-21), a biomarker for lung cancers. Importantly, it is demonstrated that this biosensor can be employed to measure the miRNA-21 expression level from human lung cancer cell (A549) lysates and worked well in 100% serum, suggesting its potential for applications in clinical diagnosis and a wide range of bioanalysis.

Uniform Au@Pt core-shell nanodendrites supported on molybdenum disulfide nanosheets for the methanol oxidation reaction.

Herein, we presented a facile seeded growth method to prepare high-quality three-dimensional (3D) Au@Pt bimetallic nanodendrite-decorated molybdenum disulfide (MoS2) nanosheets (Au@Pt/MoS2). Transmission electron microscopy (TEM) and high-resolution TEM exhibited that Au@Pt core-shell nanostructures were dispersed onto the surface of MoS2 nanosheets. More importantly, the thickness of the Pt shell of the Au@Pt bimetallic nanodendrites on the surface of the MoS2 nanosheets could be easily tuned via simply changing the synthesis parameters, such as the concentration of H2PtCl6, reaction time and temperature, which greatly influence the catalytic ability of Au@Pt/MoS2 nanohybrids. Both cyclic voltammetry (CV) and chronoamperometry (CA) demonstrated that the as-prepared Au@Pt/MoS2 nanohybrids possessed much higher electrocatalytic activity and stability than Pt/MoS2 or commercial Pt/C catalyst. The peak current mass density of the selected Au@Pt/MoS2 was 6.24 A mg(-1), which was 3389 and 20.3 times those of Pt/C (0.00184 A mg(-1)) and Pt/MoS2 (0.307 A mg(-1)), respectively. The presented method may be a facile approach for the synthesis of MoS2-supported bimetallic nanocomposites, which is significant for the development of high performance MoS2-based sensors and catalysts.

Cationic Conjugated Polymer/Hyaluronan-Doxorubicin Complex for Sensitive Fluorescence Detection of Hyaluronidase and Tumor-Targeting Drug Delivery and Imaging.

Hyaluronidase (HAase) is becoming a new type of tumor marker since it has been demonstrated to be overexpressed in various kinds of cancer cells. In this study, we described a novel fluorescence method for sensitive, rapid, and convenient HAase detection and tumor-targeting drug delivery and imaging, using a probe prepared by electrostatic assembly of a cationic conjugated polymer (CCP) and anionic hyaluronan (HA) conjugated with the anticancer drug doxorubicin (Dox). The CCP we used was poly{[9,9-bis(6'-(N,N,N-diethylmethylammonium)hexyl)-2,7-fluorenylene ethynylene]-alt-co-[2,5-bis(3'-(N,N,N-diethylmethylammonium)-1'-oxapropyl)-1,4-phenylene]} tetraiodide (PFEP). HA is a natural mucopolysaccharide that can be hydrolyzed by HAase into fragments with low molecular weights. In the PFEP/HA-Dox complex, the fluorescence of PFEP was efficiently quenched due to electron transfer from PFEP to Dox. After the PFEP/HA-Dox complex was exposed to HAase or was taken up by cancer cells through the specific binding between HA and CD44 receptor, HA was degraded by HAase to release the Dox, leading to the recovery of PFEP fluorescence to the "turn-on" state. Moreover, the degree of fluorescence recovery was quantitatively correlated with the concentrations of HAase. Compared with many previously reported methods, our work did not require laborious multiple modifications of HA that may affect the activity of HAase. This point, combined with the excellent optoelectronic property of conjugated polymer, endowed this method with high sensitivity (detection limit: 0.075 U/mL), high specificity, and rapid response, making it applicable for reliable and routine detection of HAase. This fluorescent probe was successfully utilized to detect HAase levels in human urine samples; furthermore, it can also be employed as a multifunctional system by realizing tumor-targeting drug delivery and cell imaging simultaneously. The development of this fluorescence method showed promising potential for early tumor diagnosis and therapy based on HAase detection.

Thioflavin T as an Efficient G-Quadruplex Inducer for the Highly Sensitive Detection of Thrombin Using a New Föster Resonance Energy Transfer System.

We report a new Föster resonance energy transfer (FRET) system that uses a special dye, thioflavin T (ThT), as an energy acceptor and a water-soluble conjugated polymer (CP) with high fluorescence as an energy donor. A simple, label-free, and sensitive strategy for the detection of thrombin in buffer and in diluted serum was designed based on this new system using ThT as an efficient inducer of the G-quadruplex. The difference between the blank and the positive samples was amplified due to distinctive FRET signals because thrombin has little effect on the intercalation of ThT into the G-quadruplex. In the absence of the target, ThT induces the aptamer to form a G-quadruplex and intercalates into it with strong fluorescence. The electrostatic attractions between the negatively charged G-quadruplex and positively charged CP allow a short donor-acceptor distance, resulting in a high FRET signal. However, in the presence of the target, the aptamer forms a G-quadruplex-thrombin complex first, followed by the intercalation of ThT into the G-quadruplex. A long distance exists between the donor and acceptor due to the strong steric hindrance from the large-sized thrombin, which leads to a low FRET signal. Compared with previously reported strategies based on the FRET between the CP and dye, our strategy is label-free, and the sensitivity was improved by an order of magnitude. Our strategy also shows the advantages of being simple, rapid (about 50 min), sensitive, label-free, and low-cost in comparison to strategies based on the FRET between quantum dots and dyes.

Monodispersed nanoparticles of conjugated polyelectrolyte brush with high charge density for rapid, specific and label-free detection of tumor marker.

Highly charged nanoparticles of a conjugated polyelectrolyte brush were used to sense the human α-fetoprotein (AFP) by observing selective superquenching in several minutes. The unique property of nanoparticles that the self-aggregation causes an unchanged or enhanced fluorescence can reduce the interference from non-target substance significantly.

Creating SERS hot spots on MoS(2) nanosheets with in situ grown gold nanoparticles.

Herein, a reliable surface-enhanced Raman scattering (SERS)-active substrate has been prepared by synthesizing gold nanoparticles (AuNPs)-decorated MoS2 nanocomposite. The AuNPs grew in situ on the surface of MoS2 nanosheet to form efficient SERS hot spots by a spontaneous redox reaction with tetrachloroauric acid (HAuCl4) without any reducing agent. The morphologies of MoS2 and AuNPs-decorated MoS2 nanosheet were characterized by TEM, HRTEM, and AFM. The formation of hot spots greatly depended on the ratio of MoS2 and HAuCl4. When the concentration of HAuCl4 was 2.4 mM, the as-prepared AuNPs@MoS2-3 nanocomposite exhibited a high-quality SERS activity toward probe molecule due to the generated hot spots. The spot-to-spot SERS signals showed that the relative standard deviation (RSD) in the intensity of the main Raman vibration modes (1362, 1511, and 1652 cm(-1)) of Rhodamine 6G were about 20%, which displayed good uniformity and reproducibility. The AuNPs@MoS2-based substrate was reliable, sensitive, and reproducible, which showed great potential to be an excellent SERS substrate for biological and chemical detection.

Cationic conjugated polymer/fluoresceinamine-hyaluronan complex for sensitive fluorescence detection of CD44 and tumor-targeted cell imaging.

Simple, rapid, and sensitive detection of CD44 is of paramount importance since it plays pivotal roles in tumor initiation, growth and metastasis. Herein, we describe a novel method for sensitive, visual and facile fluorescence detection of CD44 and CD44-mediated cancer cell imaging, using a probe based on cationic conjugated polymer (CCP)-PFEP and fluoresceinamine-hyaluronan (FA-HA). HA is an anionic natural glycosaminoglycan that can specifically bind to the overexpressed CD44 on various kinds of cancer cells. PFEP and FA-HA formed a complex through electronic interactions, resulting in a highly efficient fluorescence resonance energy transfer (FRET) from PFEP to FA-HA; moreover, the efficiencies of FRET correlated with the concentrations of CD44 because the specific binding of HA-CD44 would separate FA-HA away from PFEP. This method did not require laborious and expensive dual-labeling or protein-labeling needed in previously reported detection methods of CD44. Just mix the sample and test solution containing the PFEP/FA-HA complex, and the results allowed naked-eye detection by observing fluorescent color of solutions with the assistance of a UV lamp. Most importantly, the use of a conjugated polymer with excellent amplification property as well as the specific binding of HA-CD44 endowed this method with high sensitivity and specificity, making it applicable for reliable quantitative detection of CD44. Furthermore, the PFEP/FA-HA complex formed nanoparticles in aqueous solution, and the nanoparticles can be selectively taken up by MCF-7 cells (cancer cell) through the HA-CD44 interaction, thereby giving rise to a dual-color tumor-targeted imaging probe with good photostability. The development of this fluorescent probe showed promising potential to make a reliable and routine method available for early diagnosis of cancer.

Target-induced conjunction of split aptamer fragments and assembly with a water-soluble conjugated polymer for improved protein detection.

Rapid and sensitive detection of proteins is crucial to biomedical research as well as clinical diagnosis. However, so far, most detection methods rely on antibody-based assays and are usually laborious and time-consuming, with poor sensitivity. Herein, we developed a simple and sensitive fluorescence-based strategy for protein detection by using split aptamer fragments and a water-soluble polycationic polymer (poly{[9,9-bis(6'-(N,N,N-diethylmethylammonium)hexyl)-2,7-fluorenylene ethynylene]-alt-co-[2,5-bis(3'-(N,N,N-diethylmethylammonium)-1'-oxapropyl)-1,4-phenylene] tetraiodide} (PFEP)). The thrombin-binding DNA aptamer was split into two fragments for target recognition. The PFEP with high fluorescence emission was used as energy donor to amplify the signal of dye-labeled DNA probe. In the absence of target, three DNA/PFEP complexes were formed via strong electrostatic interactions, resulting in efficient Föster resonance energy transfer (FRET) between two fluorophores. While the presence of target induces a conjunction of two split aptamer fragments to form G-quadruplex, and subsequent assemble with PFEP leading to the formation of G-quadruplex/thrombin/PFEP complex. The distance between the PFEP and dye increased due to protein's large size, leading to a remarkable decrease of the FRET signal. Compared with the intact aptamer, the use of shorter split aptamer fragments increases the possibility of forming G-quadruplex upon target. Thus, the rate of change of FRET signal before and after the addition of target improved significantly and a higher sensitivity (limit of detection (LOD) = 2 nM) was obtained. This strategy is superior in that it is rapid, has low cost and homogeneous detection, and does not need heating to avoid an unfavorable secondary structure of DNA probe. With further efforts, this method could be extended to a universal way for simple and sensitive detection of a variety of biomolecules.

DNA-conjugated quantum dot nanoprobe for high-sensitivity fluorescent detection of DNA and micro-RNA.

Herein, we report a convenient approach to developing quantum dots (QDs)-based nanosensors for DNA and micro-RNA (miRNA) detection. The DNA-QDs conjugate was prepared by a ligand-exchange method. Thiol-labeled ssDNA is directly attached to the QD surface, leading to highly water-dispersible nanoconjugates. The DNA-QDs conjugate has the advantages of the excellent optical properties of QDs and well-controlled recognition properties of DNA and can be used as a nanoprobe to construct a nanosensor for nucleic acid detection. With the addition of a target nucleic acid sequence, the fluorescence intensity of QDs was quenched by an organic quencher (BHQ2) via Förster resonance energy transfer. This nanosensor can detect as low as 1 fM DNA and 10 fM miRNA. Moreover, the QDs-based nanosensor exhibited excellent selectivity. It not only can effectively distinguish single-base-mismatched and random nucleic sequences but also can recognize pre-miRNA and mature miRNA. Therefore, the nanosensor has high application potential for disease diagnosis and biological analysis.

Monodispersed grafted conjugated polyelectrolyte-stabilized magnetic nanoparticles as multifunctional platform for cellular imaging and drug delivery.

An anionic grafted conjugated polyelectrolyte was synthesized, and then magnetic nanoparticles stabilized with this material were successfully prepared by a convenient method and used for bioimaging and drug delivery. Grafted conjugated polymer (PFPAA) containing abundant carboxyl groups was attached to the surface of Fe3O4 nanoparticles through ligand exchange with oleic acid and anionic grafted conjugated polyelectrolyte-stabilized magnetic nanoparticles (MNPs@PFPANa) were then obtained by ionization with sodium carbonate. These as-synthesized nanoparticles showed good water solubility and stability, with no precipitation observed in 8 months, and had a narrow size distribution with a mean hydrodynamic diameter of 26 ± 2.4 nm. In addition, these nanoparticles exhibited superparamagnetic properties with a saturation magnetization (Ms) of 20 emu g-1, which sufficient for bioapplications. Upon 48 h incubation with macrophage cells, the obtained nanoparticles showed good biocompatibility of 2 pg Fe per cell as measured by ICP-OES. Furthermore, MNPs@PFPANa were low toxicity as confirmed by an MTT assay using NIH-3T3 fibroblasts. Confocal microscopy results revealed that MNPs@PFPANa can be retained in cytoplasm with high fluorescence. MNPs@PFPANa exhibited good DOX drug loading efficiency of about 10 wt% and showed good therapeutic efficiency for BGC-823 cancer cells. These results indicated such multifunctional nanoparticles would be useful in bioimaging and as drug carriers for cancer treatment.

An ultrasensitive label-free biosensor for assaying of sequence-specific DNA-binding protein based on amplifying fluorescent conjugated polymer.

Sensitive, reliable, and simple detection of sequence-specific DNA-binding proteins (DBP) is of paramount importance in the area of proteomics, genomics, and biomedicine. We describe herein a novel fluorescent-amplified strategy for ultrasensitive, visual, quantitative, and "turn-on" detection of DBP. A Förster resonance energy transfer (FRET) assay utilizing a cationic conjugated polymer (CCP) and an intercalating dye was designed to detect a key transcription factor, nuclear factor-kappa B (NF-κB), the model target. A series of label-free DNA probes bearing one or two protein-binding sites (PBS) were used to identify the target protein specifically. The binding DBP protects the probe from digestion by exonuclease III, resulting in high efficient FRET due to the high affinity between the intercalating dye and duplex DNA, as well as strong electrostatic interactions between the CCP and DNA probe. By using label-free hairpin DNA or double-stranded DNA containing two PBS as probe, we could detect as low as 1 pg/µL of NF-κB in HeLa nuclear extracts, which is 10000-fold more sensitive than the previously reported methods. The approach also allows naked-eye detection by observing fluorescent color of solutions with the assistance of a hand-held UV lamp. Additionally, a less than 10% relative standard deviation was obtained, which offers a new platform for superior precision, low-cost, and simple detection of DBP. The features of our optical biosensor shows promising potential for early diagnosis of many diseases and high-throughput screening of new drugs targeted to DNA-binding proteins.

DNA biosensors based on water-soluble conjugated polymers.

Conjugated polymers (CPs) with large, delocalised molecular structures exhibit unique optical and electrochemical characteristics that can be used as excellent sensing elements. Recently, research on chemical and biological sensors that use water-soluble CPs as transducers has generated intense interest. Two main sensing mechanisms are used for the detection of DNA-related events, such as hybridisation, mismatch, single nucleotide polymorphism (SNP), SNP genotyping, conformational changes, and cleavage of the nucleic acids. One mechanism takes advantage of the fluorescence resonance energy transfer (FRET) between CPs and a chromophore label on the nucleic acid probes in which a series of cationic polyfluorene, polythiophene and polyarylene derivatives are frequently used. The other mechanism relies on the conformational effects of CPs, which is induced by combination of the specific targets in which cationic polythiophene derivatives are often used. The electron transfer property of CPs are always used to design high sensitive electrochemical DNA biosensors. Here we review recent progress in the development of optical and electrochemical DNA biosensors based on water-soluble CPs.

Solvent- and pH-induced self-assembly of cationic meta-linked poly(phenylene ethynylene): effects of helix formation on amplified fluorescence quenching and Förster resonance energy transfer.

We reported here the synthesis and characterization of a novel water-soluble, meta-linked poly(phenylene ethynylene) (m-PPE-NEt(2)Me(+)) featuring quaternized side groups. We studied the solvent-induced self-assembly of m-PPE-NEt(2)Me(+) in MeOH/H(2)O solvent mixtures by using UV-vis absorption and fluorescence spectroscopies. The results showed that the polymer folded into a helical conformation and that the extent of helical folding increased with the volume % water in the solvent. This cationic polymer also exhibited unique pH-induced helix formation, which was attributed to the partial neutralization of quaternized side groups at high pH and the meta-links in the main chain of the polymer. Studies on the fluorescence quenching of m-PPE-NEt(2)Me(+) by anthraquinone-2,6-disulfonate (AQS) and Fe(CN)(6)(4-), two small-molecule anionic quenchers with different typical structures, revealed more efficient quenching of helical conformation by AQS than by Fe(CN)(6)(4-). We proposed that the two quenchers most likely interacted with the polymer helix in two different modes; that was, AQS featuring large planar aromatic ring could intercalate within adjacent π-stacked phenylene ethynylene units in the polymer helix, whereas Fe(CN)(6)(4-) mainly bound to the periphery of polymer helix through ion-pair formation. Finally, the results of FRET from the helical polymer to the fluorescein (C*)-labeled polyanions, ssDNA-C* (ssDNA: single-stranded DNA) and dsDNA-C* (dsDNA: double-stranded DNA) also suggested two different modes of interactions. As compared with the FRET to dsDNA-C*, the FRET to ssDNA-C* was slightly more efficient, which was believed to arise from the additional binding of ssDNA-C* with the polymer via intercalation of its exposed hydrophobic bases into the π stack of adjacent phenylene ethynylene units in the polymer helix.

A colorimetric strategy based on a water-soluble conjugated polymer for sensing pH-driven conformational conversion of DNA i-motif structure.

Using a water-soluble conjugated polymer (CP) as a sensing probe, we developed a rapid colorimetric detection strategy for pH-driven conformational conversion of DNA i-motif structure. Two sensing configurations were designed: one used CP only to detect the conversion between i-motif and random-coiled state of a C-rich single-strand DNA, the other used CP and a complementary single-strand DNA to investigate the conversion of duplex to i-motif equilibrium. All the conversions would lead to color change observed directly with naked eyes within a few minutes. The limitation of detection (LOD) is as low as 40 nM. More importantly, reversible conformational conversions by adjusting the pH of the system could also be detected.

Tuning backbones and side-chains of cationic conjugated polymers for optical signal amplification of fluorescent DNA detection.

Three cationic conjugated polymers (CCPs) exhibiting different backbone geometries and charge densities were used to investigate how their conjugated backbone and side chain properties, together with the transitions of DNA amphiphilic properties, interplay in the CCP/DNA-C* (DNA-C*: fluorophore-labeled DNA) complexes to influence the optical signal amplification of fluorescent DNA detection based on Förster resonance energy transfer (FRET). By examining the FRET efficiencies to dsDNA-C* (dsDNA: double-stranded DNA) and ssDNA-C* (ssDNA: single-stranded DNA) for each CCP, twisted conjugated backbones and higher charge densities were proved to facilitate electrostatic attraction in CCP/dsDNA-C* complexes, and induced improved sensitivity to DNA hybridization. Especially, by using the CCP with twisted conjugated backbone and the highest charge density, a more than 7-fold higher efficiency of FRET to dsDNA-C* was found than to ssDNA-C*, indicating a high signal amplification for discriminating between dsDNA and ssDNA. By contrast, linear conjugated backbones and lower charge density were demonstrated to favor hydrophobic interactions in CCP/ssDNA-C* complexes. These findings provided guidelines for the design of novel sensitive CCP, which can be useful to recognize many other important DNA activities involving transitions of DNA amphiphilic properties like DNA hybridization, such as specific DNA binding with ions, some secondary or tertiary structural changes of DNA, and so forth.

Unmodified gold nanoparticles as a colorimetric probe for potassium DNA aptamers.

Unmodified gold nanoparticles effectively differentiate unfolded and folded DNA, thus providing a novel approach to colorimetrically probe aptamer-based recognition processes.