The identification and monitoring of circulating tumor cells (CTCs) in human blood plays a pivotal role in the convenient diagnosis of different cancers. However, it remains a major challenge to monitor these CTCs because of their extremely low abundance in human blood. Here, we describe the synthesis of a new aptamer-functionalized and gold nanoparticle (AuNP) array-decorated magnetic graphene nanosheet recognition probe to capture and isolate rare CTCs from human whole blood. In addition, by employing the aptamer/electroactive species-loaded AuNP signal amplification probes, multiplexed electrochemical detection of these low levels of CTCs can be realized. The incubation of the probes with the sample solutions containing the target CTCs can lead to the efficient separation of the CTCs and result in the generation of two distinct voltammetric peaks on a screen-printed carbon electrode, whose potentials and current intensities, respectively, reflect the identity and number of CTCs for the multiplexed detection of the Ramos and CCRF-CEM cells with detection limits down to 4 and 3 cells mL–1. With the successful demonstration of the concept, further extension of the developed sensing strategy for the determination of various CTCs in human whole blood for the screening of different cancers can be envisioned in the near future.

Monitoring circulating tumor cells (CTCs) in human blood can offer useful information for convenient metastasis diagnosis, prognosis, and treatment of cancers. However, it remains a substantial challenge to detect CTCs because of their particular scarcity in complex peripheral blood. Herein, we describe an in situ-generated multivalent aptamer network-modified electrode interface for efficiently capturing and sensitively detecting CTCs in whole blood by electrochemistry. Such an interface was fabricated via rolling circle amplification extension of the electrode-immobilized primer/circular DNA complexes for the yield of long ssDNA strands with many repeated aptamer segments, which could achieve efficient capture of rare CTCs in a multivalent cooperative manner. The antibody and horseradish peroxidase-functionalized gold nanoparticles further specifically associated with the surface-bound CTCs and generated electrocatalytically amplified current outputs for highly sensitive detection of CTCs with an attractive detection limit of five cells. Also, the multivalent aptamer network interface could successfully distinguish the target cells from other control cells and achieve CTC detection in whole blood, demonstrating its promising potential for monitoring different rare CTCs in human blood.

The development of electronic sensors with minimized usage of reagents and washing steps in the sensing protocols will significantly facilitate the detection of biomolecules. In this work, by using a new pseudoknot design of the aptamer probes, the construction of an electronic sensor for reagentless and single-step detection of immunoglobulin E (IgE) in human serum is described. The pseudoknot aptamer probes are self-assembled on the disposable electrode surface. The association of IgE with the aptamer probes leads to conformational changes of the pseudoknot aptamer structures and brings the redox-tags in close proximity to the electrode, resulting in amplified current response for monitoring IgE. The effects of the pseudoknot structure and the immobilization concentration of the aptamer probes on the sensor performance are evaluated. Under optimal conditions, the detection limit for IgE is estimated to be 60 pM. The sensor is also selective and can be employed to detect IgE in human serum samples. The developed sensor can achieve reagentless, washing-free and low-cost (with the disposable electrode) electrochemical detection of proteins, making this device a convenient sensing platform for the monitoring of different biomarkers when coupled with the appropriate aptamer probes.

The preparation and use of a new class of signal amplification label, quantum dot (QD) layer-by-layer (LBL) assembled polystyrene microsphere composite, for amplified ultrasensitive electronic detection of uropathogen-specific DNA sequences is described. The target DNA is sandwiched between the capture probes immobilized on the magnetic beads and the signaling probes conjugated to the QD LBL assembled polystyrene beads. Because of the dramatic signal amplification by the numerous QDs involved in each single DNA binding event, subfemtomolar level detection of uropathogen-specific DNA sequences is achieved, which makes our strategy among the most sensitive electronic approach for nucleic acid-based monitoring of pathogens. Our signal amplified detection scheme could be readily expanded to monitor other important biomolecules (e.g., proteins, peptides, amino acids, cells, etc.) in ultralow levels and thus holds great potential for early diagnosis of disease biomarkers.

The presence of exonuclease III leads to direct recycling and reuse of the target DNA, which in turn results in substantial signal amplification for highly sensitive, label-free impedimetric detection of specific DNA sequences.

Because of their irreversible toxicological impacts on the environment and human body, the development of reliable and sensitive Hg detection methods with high selectivity is of great significance. On the basis of the substantial signal amplification by metallo-toehold-triggered, catalytic hairpin assembly (CHA) formation of three-way DNAzyme junctions, we have constructed a highly selective and sensitive fluorescent sensing system for the determination of Hg in different environmental water samples. The presence of the target Hg ions can lead to the generation of T-Hg-T base mismatched metallo-toeholds, which trigger the catalytic assembly of three split-DNAzyme containing hairpins to form many Mg-dependent DNAzyme junction structures upon binding to the fluorescently quenched substrate sequences. The Mg ions then cyclically cleave the fluorescently quenched substrate sequences of the Mg-dependent DNAzymes to generate drastically enhanced fluorescent signals for sensitively detecting Hg at the low 4.5 pM level. The developed sensing method offers high selectivity toward the target Hg over other possible competing metal ions due to the specific T-Hg-T bridge structure chemistry in the metallo-toehold domain, and reliable detection of spiked Hg in environmentally relevant water samples with this method is also verified. Considering the nucleic acid nature of the trigger and assembly sequences, the developed approach thus holds great potentials for designing new enzyme-free signal amplification strategies to achieve highly sensitive determination of different DNA and RNA targets.

No abstract

In this work, by incorporating a specific DNAzyme sequence into a hairpin aptamer probe, we describe a label-free and sensitive method for electrochemical detection of cytokines using recombinant human IFN-γ as the model analyte. The hairpin aptamer probes are immobilized on a gold electrode through self-assembly. The presence of IFN-γ opens the hairpin structure and forms the hemin/G-quadruplex peroxidase-mimicking DNAzyme with subsequent addition of hemin. The peroxidase-mimicking DNAzyme catalyzes the electro-reduction of H(2)O(2) and amplifies the current response for IFN-γ detection, which enables the monitoring of IFN-γ at the sub-nanomolar level. The proposed sensor also shows high selectivity towards the target analyte. Our strategy thus opens new opportunities for label-free and amplified detection of different types of cytokines.