Journal of Nanomedicine Research A Review on Aptamer-Conjugated Quantum Dot Nanosystems for Cancer Imaging and Theranostic Submit Manuscript | http://medcraveonline.com Volume 5 Issue 3 - 2017 1 Tabriz University of medical Sciences, Iran 2 Department of Analytical Chemistry, University of Tabriz, Iran 3 Department of Medicinal Chemistry and drug discovery, Ardabil University of Medical Sciences, Iran *Corresponding author: Mohammad Johari Ahar, Department of Medicinal Chemistry and drug discovery, Faculty of Pharmacy, Ardabil University of Medical Sciences, Iran, Tel: +98-45-33522437-39; Fax: +98-45-33522197, Email: Received: March 10, 2017 | Published: April 18, 2017 Mini Review J Nanomed Res 2017, 5(3): 00117 Abstract Over the last 10 years, fluorescent semiconductor QD (quantum dot)-aptamer conjugates have emerged as an efficient platform for cancer imaging and therapy in animal models and in vitro. In addition, these conjugates show potential in a wide range of applications in environmental monitoring, disease diagnosis, and bio-sensing. The present review represents the recent developments in QD- aptamer bio-conjugates for applications in cancer studies. It starts with a brief introduction to Semiconductor Quantum dots (QDs), bio-conjugation of QDs and aptamer molecules, and advantages-disadvantages of using these novel tools for biochemical applications. Keywords: Theranostic; Aptamer; Cancer; Quantum dot; Imaging Abbreviations: PET: Positron Emission Tomography; MRI: Magnetic Resonance Imaging; CT: Computed Tomography; QD: Quantum Dot Introduction Cancer diagnosis and therapy remains a major obstacle worldwide. An increasing rate of cancer mortality is expected to growth to about 13 million deaths per year by 2030 [1]. Currently, six powerful diagnostic modalities including computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET-scan), single-photon emission CT, ultrasound and optical imaging are available for cancer imaging and staging [2]. However, classifying the cancers and delivering proper dosages with maximum therapeutic effects and minimum toxicity of therapeutics are the main hurdles that seems clinicians have to overcome in the field of cancer treatment. In addition, immune-editing process supporting cancer cells in escaping from the human immune system help tumor cells survive and metastasize other organs [3]. In recent two decades, nanotechnology as an emerging scientific discipline has received significant attention in all areas of science encompassing chemistry, physics and biology [4]. Indeed, nanotechnology is ever more firming a foothold in medicine, especially in oncology [5]. Nanoparticles such as quantum dots and superparamagnetic iron oxide (SPIO) are useful contrast agents for medical imaging with CT or MRI in animal studies [6]. Among quantum dots, fluorescent inorganic quantum dots (QDs) with diameter of 2 to 10 nm display superior fluorescent properties without photo-bleaching in comparing with organic fluorophores [7]. Significant evidences suggest that QDs can be used in imaging [8]. It seems that one potential area of application would be in the development of advanced materials for early diagnosis or convergence of imaging and therapy (theranostic) of cancer. Fluorescent Semiconductor Quantum dots (QDs) QDs are nanocrystals whose size-tunable fluorescence can cover electromagnetic spectrum generally from the ultraviolet (UV) to the near infrared (NIR) regions [9]. As a rule, QDs with a large diameter emit fluorescence in red region, whilst QDs with a smaller diameter radiate photons in the blue region [10]. Narrow and symmetric emission peaks obtained by excitation with broad ranges of wavelengths render multicolored single QD that enables multimodal cancer imaging [11]. For this reason, these QDs can be suggested as a potential candidate multimodal optical imaging, especially in the near infrared region (NIR), for human studies [12]. The term of QD is generally supposed of spherical nanocrystals in the size ranges of 1-10 nm diameter [13], but it can be produced in the other shapes such as rods and tetrapod [14]; however, the most widely used QDs for biological applications are spherical, and will be the focus of the current review article. Bulk semiconductor physics Based on electrical conductivity, solid state physics classifies materials into three categories: insulators, semiconductors, and conductors (Figure 1). The conductivity is generally expressed as the difference in energy between the valence and conduction bands. The valence band has the highest energy level which is occupied with electrons at room temperature. Likewise, the conduction is the lowest energy electronic state that may be occupied by thermal excitation. An electron in the valence band by gaining energy (by the absorption of a photon or thermally) can enter the conduction band and leave a positively charged