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Ultrasensitive, rapid and selective diagnostic probes are urgently needed to overcome the limitations of traditional probes for norovirus (NV). Here, we report the detection of NV genogroup II via nucleic acid hybridization technology using a quantum dot (QD)-conjugated molecular beacon (MB) probe. To boost the sensitivity of the MB assay system, an ultrasensitive QD fluorophore with unique optical properties was synthesized, characterized and exploited as a fluorescence signal generator. Alloyed thioglycolic (TGA)-capped CdZnSeS QDs with a high photoluminescence (PL) quantum yield (QY) value of 92% were synthesized, and a modified silanization method was employed to encapsulate the thiol-capped QDs in a silica layer. The resulting highly luminescent alloyed SiO2-coated CdZnSeS QDs had a remarkable PL QY value of 98%. Transmission electron microscopy and dynamic light scattering confirmed the monodispersity of the alloyed nanocrystals, and zeta potential analysis confirmed their colloidal stability. Powder X-ray diffraction and PL lifetime measurements confirmed the surface modification of the QDs. The alloyed TGA-capped and SiO2-coated CdZnSeS QD-conjugated MB bioprobes detected extremely low concentrations of NV RNA. Ultrasensitive detection of low concentrations of NV RNA with a limit of detection (LOD) of 8.2copies/mL in human serum and a LOD of 9.3 copies/mL in buffer was achieved using the SiO2-coated CdZnSeS QD-MB probes, an increase in sensitivity of 3-fold compared with the detection limit for NV RNA using TGA-capped CdZnSeS QD-MBs. The additional merits of our detection system are rapidity, specificity and improved sensitivity over conventional molecular test probes.

30Controlling and engineering the particle composition of semiconductor alloy is one of 31 the topmost targets in the field of semiconductor material science and technology. 32 Quantum dot (QD) nanocrystals offer an unmatched opportunity to obtain a wide 33 range of composition-controlled alloys and have captivated a great deal of interest 34 recently. Here we report on the band gap engineering via tuning and control of the 35 sulphur molar fraction (ternary shell layer) of quaternary/ternary core/shell alloyed 36 CdZnSeS/ZnSeS QDs. Varying optical properties were exhibited by the alloyed QDs 37 but a uniform particle size distribution was maintained across all compositions. The 38 alloyed QDs displayed bright emission colours under UV irradiation whilst the 39 photoluminescence quantum yield (PL QY) were in a remarkable range of 36 -98%. 40 Non-linearity of the lattice parameter was an indication of gradient alloying of the 41 nanocrystals while kinetics of the optical properties unravelled the effect of intrinsic 42 optical bowing. The displacement of bond length and anion mismatch influenced the 43 optical properties of the QDs with respect to the PL QY variation. Alloyed 44 CdZnSeS/ZnSe 1.0 S 1.3 QDs with a spectacular PL QY value was exploited as an 45 ultrasensitive fluorescence reporter in a conjugated molecular beacon (MB) assay to 46 detect influenza virus H1N1 RNA. Our detection system was rapid, highly sensitive 47 to detect extremely low concentrations of H1N1 RNA (down to 2 copies/mL), specific 48 and versatile (detects H1N1 RNA in human serum). For proof of concept, the alloyed 49 CdZnSeS/ZnSe 1.0 S 1.3 QD-MB bioprobe exhibited a superior 12-fold sensitivity over 50 alloyed CdZnSeS-MB probe while conventional CdSe/ZnS-MB probe could not detect 51 the extremely low concentrations of influenza virus H1N1 RNA. 52 3 KEYWORDS: Quantum dots, alloy, influenza virus, RNA, photoluminescence, 53 molecular beacon 54 55 1. Introduction 56 At the nanoscale, a great deal of attention has been ascribed to band gap engineering 57 as a powerful tool in the fabrication of semiconductor quantum dots (QDs) 58 nanocrystals. 1-4 Conventional method of tuning the semiconductor band gap is by 59 altering the QDs size in a process known as quantum confinement. QDs produced by 60 size confinement have found application in a wide array of fields, such as in biological 61 imaging, photovoltaics, catalysis, optoelectronics, sensor/biosensor and drug 62 delivery systems, etc. 5-8 In many applications, QDs of small size are required to obtain 63 distinct data, however, the significant size difference between QDs of different 64 emission colors poses a serious problem in device processing, superlattice structure 65 formation and biomolecule conjugation. 9,10 Hence, tuning the optical properties of 66 QDs independent of their size is highly needed to circumvent this problem. 67 An alternative means of engineering the band gap of QD nanocrystals is via 68 control and alteration of the particle composition with respect to ch...

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