Cdte Quantum Dots/Poly (Diallyl Dimethyl Ammonium Chloride) Multilayer Films: Preparation And Application For Gaseous Sensors

A trend in current sensor development is miniaturization to obtain inexpensive and compact gas sensors that are robust and safe, have low power consumption and enable multiplexing of sensor arrays and remote sensing [1, 2]. Gas sensors play a key role in a variety of fields , such as environmental pollution monitoring, industrial process monitoring, leak detection of explosive gases, and medical breath analysis. In order to increase sensitivity, devices with nanostructure for gas sensors has shown lots of advantages[3].

 From previous literatures, we can find that there are many gas detecting methods so far. But, compared with those traditional gas detection techniques, which are often costly, low sensitivity and time-consuming, semiconductor sensors have drawn a great deal of attention in recent years for its unique optical advantages. Semiconductor luminescent nanocrystals, known as “quantum dots” (QDs), exhibit unique optical and electronic properties, including high luminescent quantum yields, tunable emission, high photostability and relatively long emission lifetime. All these advantages explain the reason of its presence [4]. Furthermore, it has been used for energy conversion and storage[5 -8], fabrication of optoelectronic device[9], and particularly, sensor applications[10 -12]. 

Recently, a number of QD -based sensors have been reported for ions, [13] biomacromolecules, [14-16] and small organic molecules. [17] And, CdTe QDs have been proved to be a promising material as elemental building blocks for the next generation of nanodevices [18, 19]. Self -assembled multilayers by layer-by-layer (LBL) method are stable, well -ordered, easy to prepare and low cost, and have been extensively applied for the constructions of chemo - and bio -sensors [20, 21 ]. Another important feature of LBL is recharging of the surface at every step of the adsorption self -assembly, which results in oppositely charged molecules to be adsorbed in the next step with molecular  order during the films fabrication process. Therefore the stable LBL method can encapsulate the QDs efficiently into flexible nanofilms (thickness below 60 nm) [22]. It has been also successfully applied to the preparation of multiplayer films of polyelectrolytes with other materials such as proteins, graphite oxides, gold colloids, dyes and nanoparticles [23]. Many groups have developed QDs-based sensing systems for the detection of Hg2+ [24-26]  and Cu2+ [27-29] based on the fluorescence quenching of QDs.  

In this paper, CdTe QDs multilayer films was fabricated by the standard LBL assembly technique. The CdTe nanoparticles with negative charged in the presence of MPA can serve as the anionic entity needed in the multilayer fabrication technique. Besides, The effects of assembling methods, concentration of PDDA and layer number of films on fluorescence intensity of QDMF have been studied.