• Artificially synthesized fluorescent nano particles have manifold potential applications in the manufacturing of electrooptics, optical data storage, as well as for biochemical, bioanalytical and medical applications.
• Sonication is an effective and reliable method to synthesize fluorescent nano particles of high quality on industrial scale.
• The ultrasonic synthesis of fluorescent nano particles is simple, safe, reproducible and scalable.

Ultrasonic Preparation of Fluorescent Nano Particles

The application of ultrasonic waves to nano materials is well known for its beneficial effects, which include the sonochemical synthesis of nano particles, their functionalization and modification. Beside these sonochemical applications, ultrasound is the preferred technique for a reliable and effective dispersion and deagglomeration of stable nano suspensions.

Ultrasonic Preparation of Fluorescent Nanoparticles

Ultrasonication is a proven tool improving the colloidal synthesis of uniform and highly crystalline nanoparticles with fluorescent properties, high quantum efficiency and stability.
Ultrasonic assists during:

• Synthesis
• Functionalization
• Modification
• Dispersion
• Deagglomeration & Detangling

Water-Soluble Carbon Nanoparticles with Fluorescence Up-Conversion

Li et al (2010) have developed a one-step ultrasonic method to synthesize monodispersed water-soluble fluorescent carbon nanoparticles (CNPs). The fluorescent particles were synthesized directly from glucose by a one-step alkali or acid assisted ultrasonic treatment. The particle surfaces were rich in hydroxyl groups, giving them high hydrophilicity. The CNPs could emit bright and colorful photoluminescence covering the entire visible-to-near infrared (NIR) spectral range. Furthermore, these CNPs also had excellent up-conversion fluorescent properties.
The one-step ultrasonic reaction process is a green and convenient method using natural precursors to prepare ultra small sized CNPs by using glucose as carbon resource. The CNPs exhibit stable (>6 months) and strong PL (quantum yield ∼7%), especially two excellent photoluminescent properties: NIR emission and up-conversion photoluminescent properties. Combining free dispersion in water (without any surface modifications) and attractive photoluminescent properties, these CNPs are promising for a new type of fluorescence markers, bio-sensors, biomedical imaging, and drug delivery for applications in bioscience and nano-biotechnology.

(a) TEM image of CNPs prepared via sonication from glucose with diameter less than 5 nm; (b), (c) Photographs of CNPs dispersions in water with sunlight and UV (365 nm, center) illumination, respectively; (d-g) Fluorescent microscope images of CNPs under different excitation: d, e, f, and g for 360, 390, 470, and 540 nm, respectively. [Li et al. 2010]

Fluorescent Porphyrin Nano Particles

The research group of Kashani-Motlagh has successfully synthesized fluorescent porphyrin nanoparticles under ultrasonication. Therefore, they combined precipitation and sonication. The resulting [tetrakis(para-chlorophenyl)porphyrin] TClPP nanoparticles were stable in solution without agglomeration for at least 30 days. No self aggregation of the constituent porphyrin chromophores was observed. The TClPP nanoparticles exhibited interesting optical properties, particularly a large bathochromic shift in the absorption spectra.
The duration of the ultrasonic treatment has profound effects on the particle size of the porphyrin nanoparticles. At shorter sonication times, the porphyrin nanoparticles have sharper peaks and stronger absorbances; this indicates that by increasing the time of sonication, the number of porphyrin nanoparticles becomes more and the number of porphyrins per each unit of nanoparticle increases.

The research group of Kashani-Motlagh (2010) found a simple ultrasonic precipitation route to synthesize fluorescent prophyrin nano particles.

Synthesis of Magnetic/Fluorescent Nanocomposites

Ultrasonically assists the synthesis of nanocomposites consisting of magnetic nanoparticles and fluorescent quantum dots (QDs) with a coating of silica shell. These composites are bifunctional, featuring the advantages of both QDs and magnetic nano particles. CdS quantum dots were synthesized by the following procedure: At first, 2 mL of the nucleation film underlayer containing ferro magnetofluid and 0.5 mL of 1 mol/L CdS quantum dots were blended under ultrasonic stirring, 2 mL PTEOS (pre-polymerized tetraethylorthosilicate) was then added to the previous mixture, and finally 5 mL ammonia was added.
Furthermore, ultrasonic emulsification allows for the preparation of new multi-colors high fluorescent-superparamagnetic nanoparticles using quantum dots (QDS) and magnetite nanoparticles and amphiphilic poly(tertbutyl acrylate-co-ethyl acrylate-co-methacrylic acid) tribloc copolymer for the encapsulation.