Advances in the study of quantum dots as biofluorescent markers.

In order to understand the structure of various reactions in organisms, it is necessary to monitor the interactions of various
proteins
or cells in organisms, which in the past were mainly achieved by labeling cells and bions with
isotopes
and
organic
fluorescent dyes. But isotopes and organic dyes are known to have a series of defects that limit their use in living organisms. The emergence of quantum dots solves this problem and has great hopes of becoming a new generation of biofluorescent markers.
quantum dots ( QDs ) , also known as semiconductor nanocrystals ( Semiconductor nanocrystals ) , are nanoparticles consisting of elements of II.-VI. family (e.g. CdSe, CdTe, CdS, ZnSe, etc.) or III.V. family (e.g. InP, InAs, etc.). Quantum dots are generally sperical crystals with diameters of 1-10nm, and there have been reports of them as rods and four-foot cones, but spter quantum dots are most widely used in biology. Therefore, this paper will focus on the sperical quantum dots around the optical characteristics of quantum dots, preparation methods and their research progress as fluorescent markers in biology for a brief review.
1, the optical properties of quantum dots
compared to traditional organic fluorescent dyes or molybons, fluorescent quantum dots have the following optical characteristics: (1) the emission wavelength of quantum dots can be "tuned" by controlling their particle size, resulting in a variety of distinguished colors. In the case of cdSe nanoparticles in the ZnS package, blue light is emitted when the cdSe core diameter is 1.8nm, and red light is emitted when the cdSe core diameter is 7nm, and fluorescence from CDSe of different sizes can cover the entire visible
spectral
. (2) Nanocrystals of different sizes can be excited by light of the same wavelength and emit different colors of light, and their excitation spectrum is wide and continuously distributed, while the emission spectrum is symmetrically distributed and narrow in width, so that different quantum dots can be excited by light of the same wavelength and allow biomarkers to be made using quantum dots of different spectra at the same time. The different fluorescent dye molecules need multiple excitation wavelengths, and the excitation spectrum is narrow, the emission spectrum is wide, the spectrum of different color fluorescent molecules easily overlaps with each other, so it is difficult to use more than two fluorescence points at the same time for multi-
color label
. (3) Quantum dots have good photochemical stability and can withstand stronger excitation light and longer light emission cycles. Dye fluorescent molecules typically have an excitation and emission cycle of only a few minutes, while quantum dots typically last several hours, such as the ZnS package by cdS quantum dot stability is 100 times that of Rodamine 6G.
2, quantum dot synthesis
2.1 synthesis method
for the quantum point of biofluorescent probe, there are currently two main synthesis methods: one is in the water phase synthesis, the other is the use of collosic chemistry method in the organic phase synthesis. Prior to 1993, quantum dots were mainly produced by adding
stabilizers
e.g. glyceroglyceal, polyphosphate, etc.) to aqueous solutions. In recent years, there have also been reports of the synthesis of quantum dots in aqueous solutions, such as Lin using -based propyl acrylic acid as a stabilizer, which synthesizes CDTe semiconductor nanoparticles directly in aqueous solutions by electrostation. The direct synthesis of quantum dots in aqueous solution is simple to operate, and the materials used are low in price and less toxic. However, the fluorescence yield of quantum dots synthesized in aqueous solutions is very low, and the size distribution range of quantum dots is large (compared to the standard error RSD >15%).
scientists have made many attempts to completely solve the shortcomings of low fluorescence yield and wide size distribution of synthetic quantum dots in aqueous solutions, so in recent years, people have increasingly used to synthesize quantum dots in organic systems. In 1993, Murray and others (CH
3
)
2
Cd and TOPSe (Trioctylphospine selenide) were synthesized as presumps in a high-temperature toxinous phosphorus oxide (TOPO) solution. This method produces well-structured quantum dots and smaller dimensional variation coefficients (RSD<5%), but its fluorescence yield is still very low (about 10%). Later, it was found that a layer of ZnS on the quantum dot table bread significantly increased quantum yield at the quantum dot. In 1996, Hines and others synthesized cdSe quantum dots covered with ZnS, which significantly increased fluorescence yield at room temperature. On this basis, Dabbousi and others coated their prepared single dispersed CdSe nanoparticle surface bread with a layer of ZnS, and increased its quantum yield to 30%-50%. Recently, Peng et al. have improved traditional synthesis methods by using CdO as raw material to synthesize cdS, CdSe, cdTe nanocrystals with high fluorescence yields. Compared with the traditional nuclear/shell nanoparticles, the quantum dots synthesized by this method also have very high quantum yield without surface bread.
2.2 Preparation of water-soluble quantum dots
Quantum dots are prepared in organic systems using collosic chemistry, and their hydrophobic surface limits the application of quantum dots in biological environments. Quantum dots, which are difficult to obtain biocompasitiveity, are also the biggest problem that restricts the application of quantum dots in biological science. Therefore, before being coupled with biomoplements, it is necessary to modify its surface with a certain dual-functional base group, so that it has a certain water solubility and can be coupled with biomolymes. Through continuous efforts, scientists have developed several methods for preparing water-soluble quantum dots.
Bruchez and others first reported the preparation of water-soluble quantum dots, replacing topo molecules on CDS-protected ZnS quantum dots directly with 3-(-based propylene) trioxymethylene (MPS) and then using trioxymethylene water The solution, then on the surface of the quantum dot formed a layer with silicon dioxide / silica shell, and then the quantum dot with some dual-function methyl
compounds
(e.g. amino propylene triamoxysilane, methylene oxide propylene, etc.) reaction, then made a water-soluble quantum point. Another way to prepare water-soluble quantum dots is to directly adsorption some dual-functional base, such as Chan, by adding -base acetic acid and an organic base to a chloroform solution at toppopass-protected quantum dots, where the organic base grabs -base and pyridine-based protons. After the go, cd
2 plus
and Zn
2 plus
on the surface of the quantum dot can be combined with -based acetic acid by electrostitectric gravity, and the quantum dot can be precipitated from an organic solvent to obtain a water-soluble quantum dot.
Silaneized QDs have good stability, but only micrograms of quantum dots can be produced at a time, and under neutral pH conditions, the residual silicon oxygen base on the surface of the quantum dots can easily lead to gel or precipitation generation. Accordingly, although several grams of water-soluble quantum dots can be obtained each time by direct adsorption of -based acetic acid, -based acetic acid is unstable and easily dissociated from the surface of the quantum dot, resulting in quantum dot reunification and precipitation. To resolve these contradictions, the researchers have explored two other preparation methods: one is to make a layer of protein in the quantum dot surface bread through hydrophobic action and ion interaction, and the preliminary results show that the QDs of the protein package can be stored steadily in the buffer for at least two years, with a quantum yield similar to that produced in chloroform; In the pores of polymer pelets, such as Deubertret, the ZnS quantum dots without any surface changes are loaded directly into the hydrophosphate cores composed of a mixture of polyglycol (PEG), phosphatidyl ethanolamine (PE) and phosphatidylcholine (PC), so that the quantum dot micropopsies are uniform in size and shape, and there is almost no reunion.
.