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Sensors & Transducers Journal, Vol. 113, Issue 2, February 2010, pp. 1-17

Due to its biocompatibility and biodegradability properties, PS can be injected inside the body which over time releases it without any harm. Current research targets on how to find out the possible applications of PS as a biodegradable material in the field of medicine, for slow release of drugs or essential trace elements for in vivo applications [84]. PS can be used to treat everything from broken bones to cancer. Label –free optical biosensor using PS for detection of immunoglobulin G (IgG) in serum and whole blood sample were also reported [105]. Salonel and his co-workers [116] studied the effect of size reduction of PS particles from micro to nanosize, which affects in vitro cytotoxicity and biochemical mechanism of toxicity when these PS particles are applied to human cells. According to their findings, this cytotoxicity depends on the particle size and also on the surface chemistry of the PS particles.

Porous silicon has potential of several nanomedical applications, particularly, as a biomaterial in cancer detection because of its property of reflectivity and its resistance to stomach acid. Reflectivity of PS increases in the presence of cancer related chemicals in the blood, which indicate possible growth of tumors in the body. A silicon capsule containing the required drug can thus be directly administered orally to reach colon through the stomach without biodegradation therein [110].

3.3. Silicon Nanoparticle Sensors

To prepare Si nanoparticles, first PS is obtained by electrochemical etching of single-crystal silicon wafers in ethanolic HF solution. This PS layer was then lifted off and ultrasonicated to get silicon nanocrystals. A silicon oxide layer then grows on these nano crystals. These crystals, in aqueous solution, generate visible luminescence at room temperature due to quantum confinement effect.

In the case of medical or biological imaging, dyes are used as markers, which are not photostable. The dyes can break down under photoexcitation or visible light or at higher temperatures. The amazing property of visible room temperature luminescence of PS created an interest among the scientists for synthesizing and characterizing silicon nanoparticles. In addition to its luminescence property, PS is biocompatible and stable against photobleaching. These properties are ideal for replacing fluorescent dyes with silicon nanoparticles. Silicon nanoparticles can even replace highly toxic cadmium quantum dots for in vivo applications [92]. For biomedical applications, it is essential that they have high stability, a substantial photoluminescence quantum yield in the visible region, and solubility in aqueous media. Nanomaterials that can circulate inside the body, have great advantage for disease diagnosis and treatment. These nanomaterials ought to be harmlessly eliminated from the body shortly after they carry out their diagnostic or therapeutic functions.

Nanoparticle-based sensors and drug delivery systems have considerable potential for various types of medical treatment. The important technological advantages of nanoparticles used as drug carriers are high stability, high carrier capacity, feasibility of incorporation of both hydrophilic and hydrophobic substances, and feasibility of variable routes of administration, including oral application and inhalation. Nanoparticles can also be designed to allow controlled (sustained) drug release [92] from the matrix. These properties of nanoparticles enable improvement of drug bioavailability and reduction of the dosing frequency, and may resolve the problem of nonadherence to prescribed therapy.

Despite efforts to improve their targeting efficiency, significant quantities of systematically administered nanomaterials are cleared by the mononuclear phagocytic system before finding their targets, increasing the likelihood of unintended acute or chronic toxicity. However, there has been little effort to engineer for self-destruction of errant nanoparticles into non-toxic, systematically eliminated products. M. J. Sailor and his group [92] showed that luminescent porous silicon nanoparticles (LPSiNPs) producing near infrared luminescence can be used as drug payload for in vivo monitoring.


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