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In this study, highly efficient ECL luminophores composed of iridium complex-based nanowires (Ir-NCDs) were synthesized via covalently linking bis(2-phenylpyridine)-(4-carboxypropyl-2,2'-bipyridyl) iridium(III) hexafluorophosphate with nitrogen-doped carbon quantum dots (NCDs). The ECL intensity of the nanowires showed a five-fold increase in ECL intensity compared with the iridium complex monomer under the same experimental conditions. A label-free ECL biosensing platform based on Ir-NCDs was established for Salmonella enteritidis (SE) detection. The ECL signal was quenched linearly in the range of 10 2 -10 8 CFU/mL for SE with a detection limit of 10 2 CFU/mL. Moreover, the relative standard deviations (RSD) of the stability within and between batches were 0.98% and 3.9%, respectively. In addition, the proposed sensor showed high sensitivity, selectivity and stability towards SE in sheep feces samples with satisfactory results. In summary, the excellent ECL efficiency of Ir-NCDs demonstrates the prospects for Ir(III) complexes in bioanalytical applications.

Electrochemiluminescence (ECL) has received considerable attention as a powerful analytical technique for the sensitive and accurate detection of biological analytes owing to its high sensitivity and selectivity and wide dynamic range. To satisfy the growing demand for ultrasensitive analysis techniques with high efficiency and accuracy in complex real sample matrices, considerable efforts have been dedicated to developing ECL strategies to improve the sensitivity of bioanalysis. As one of the most effective approaches, diverse signal amplification strategies have been integrated with ECL biosensors to achieve desirable analytical performance. This review summarizes the recent advances in ECL biosensing based on various signal amplification strategies, including DNA-assisted amplification strategies, efficient ECL luminophores, surface-enhanced electrochemiluminescence, and ratiometric strategies. Sensitivity-enhancing strategies and bio-related applications are discussed in detail. Moreover, the future trends and challenges of ECL biosensors are discussed.

Recently we have demonstrated that the surface plasmon of noble metal nanoparticles can effectively enhance the ECL intensity of Ru(bpy) 3 2+ , and we named this detection principle as surface-enhanced electrochemiluminescence (SEECL-I). However, SEECL based on photomultiplier tube (PMT) detection can only detect one target at a time, which is not suitable for multiple targets detection. In this work, we combined our previous developed SEECL with a bioimaging device to develop a novel multiplexed immunassay for simultaneous and fast analysis of cancer markers. A core-shell nanocomposite consisted of gold-silicon dioxide nanoparticles doped with Ru(bpy) 3 2+ (Au@SiO 2 -Ru) with strong ECL emission was employed as ECL label due to the localized surface plasmon resonance (LSPR) of AuNPs, which can significantly enhance the ECL emission of Ru(bpy )3 2+ . The ECL signals from the 4 × 4 electrode arrays were collected using the constant potential method (current-time curve method) imaging with a sCOMS camera. As a proof-of-concept application, we demonstrated the use of the proposed SEECL-I for simultaneous detection of carcinoembryonic antigen (CEA), neuron specific enolase (NSE), and squamous cell carcinoma antigen (SCC) in exhaled breath condensates (EBCs) with low detection limit (LOD) of 0.17, 0.33, and 0.33 pg/mL (S/N = 3), respectively. The results demonstrated that the proposed SEECL-I strategy can provide a high sensitivity, fast analysis, and high-throughput platform for clinical diagnosis of cancer markers in EBCs.