Magnetic Microparticles with Silica Shell for Acid Stability
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Solution Overview
Problem
Existing magnetic particles used in biochemical and medical applications face challenges with stability, particularly in acidic and alkaline environments, and have limited surface area and scalability issues due to insufficient coating and manufacturing processes.
Innovation Solution
Development of magnetically separable microparticles with reversible magnetic properties, where nanoparticles are embedded in a SiO2 matrix with a specific composition and structure, providing enhanced stability and surface area, and a method involving pH adjustment, stabilization, and precipitation to achieve particles with diameters up to 5 µm and a large surface area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If magnetic nanoparticles are provided with a coating of silicic acid derivatives or embedded in a silicon dioxide matrix using wet-chemical syntheses, then the particles gain protection against oxidation and improved stability, but the acid stability remains insufficient and the surface area is limited
Solution Approach 1:
The patent applies porous silicon dioxide matrix with controlled pore structure to embed magnetic nanoparticles. The porous structure provides both protection (improving stability) and increased internal surface area for enhanced functionality, resolving the contradiction between stability and surface area limitations of conventional dense coatings
Solution Approach 2:
The patent creates composite particles consisting of magnetic nanoparticles embedded in a silicon dioxide matrix with specific pore characteristics. This composite structure combines the magnetic properties of the core particles with the protective and surface-area-enhancing properties of the porous silica matrix, simultaneously achieving both stability and increased surface area
2Adaptability or versatility
If complexing or chelating agents are used to modify the surface of uncoated magnetic particles, then functional groups are provided for specific applications, but too strong bonding may partially dissolve the particles or change their structure
Solution Approach 1:
The patent uses the porous silicon dioxide matrix as an intermediary layer between the magnetic nanoparticles and the complexing/chelating agents. This intermediate matrix allows functional groups to be introduced for specific applications while preventing direct strong bonding between the agents and the magnetic particles, thus avoiding particle dissolution or structural changes
Solution Approach 2:
The patent applies functional groups locally on the outer surface of the porous silicon dioxide matrix rather than directly on the magnetic nanoparticles. This localized functionalization provides the necessary adaptability for specific applications while keeping the magnetic particle core intact and structurally stable
3Ease of manufacture
If TEOS hydrolysis is used to coat magnetizable particles, then a silica coating is formed, but the particles dissolve in concentrated hydrochloric acid after only 4 minutes
Solution Approach 1:
The patent employs a porous silicon dioxide matrix structure that provides enhanced acid stability compared to conventional dense silica coatings from TEOS hydrolysis. The controlled pore structure creates a more resistant barrier against acid penetration, extending particle stability in concentrated hydrochloric acid from 4 minutes to significantly longer periods
Solution Approach 2:
The patent modifies the physical and chemical parameters of the silicon dioxide matrix, specifically creating a porous structure with controlled pore size and distribution. This parameter change transforms the matrix from a simple dense coating to a structured porous material with superior acid resistance while maintaining ease of manufacture through established sol-gel processes
4Reliability
If magnetic particles are used in colloidal form, then they remain stable in media, but they cannot be separated by applying a magnetic field
Solution Approach 1:
The patent segments the magnetic particles by embedding multiple small magnetic nanoparticles within each porous silicon dioxide matrix shell. This segmentation allows the outer colloidal particles to remain stable in media while the internal magnetic cores retain their magnetic separability, as the magnetic nanoparticles can still respond to external magnetic fields despite being enclosed
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The resulting particles demonstrate improved acid and base stability, increased surface area, and scalability, allowing for effective magnetic separation and applications in biochemistry and biomedicine with enhanced recyclability and functionalization capabilities.
Implementation Method 1
particles which can be separated from liquid media with the aid of magnetic field gradients
Implementation Method 2
A surface coating or matrix should therefore protect against oxidation processes and other attacks by this medium
Implementation Method 3
involving pH adjustment, stabilization, and precipitation
Implementation Method 4
Effecting a precipitation of the magnetically separable particles by adding a silica-forming agent
Data Source
Figure 1~3
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AI summary
The invention relates to magnetically separable particles, each comprising a plurality of nanoparticles with reversible magnetic properties and a matrix having an inorganic portion between 70 and 100 wt%, relative to the weight of the matrix, wherein the inorganic portion of the matrix consists of 80 to 100 wt% SiO2, characterised in that a. the particles have an average diameter in at least one direction of at least 5 mum, b. the particles have a surface area (according to BET measurement) of at least 1 m2/g and a (cumulative) pore volume of less than 0.195 cm3/g (ml/g), c. there is a loss of material from the nanoparticles with reversible magnetic properties of less than 2 wt% when the magnetically separable particles are stirred for 12 hours in acidic and alkaline solutions with a pH value of 1 and 12 respectively. These particles can be produced by a method comprising the following steps: a. provision of a fluid magnetic sol which was peptised by lowering the pH value to a value of not more than pH 2.5 by adding an acid; b. stabilising the sol by adding an organic complexing agent; c. adding ammonia or a compound having at least one amine function, or releasing such a function under the effect of thermal energy, to the stabilised sol in a quantity such that - optionally after the effect of the necessary thermal energy - a pH value of at least 9 is achieved; and d. effecting a precipitation of the magnetically separable particles by adding a silicon dioxide-forming agent to the stabilised sol, wherein the organic complexing agent is selected from monomeric and oligomeric hydroxycarboxylic acids with 1 to 3 hydroxy and 1 to 3 carboxylic acid functions, di-or oligocarboxylic acids and bis- or oligoalcohols with at most 8 functional groups suitable for complex formation, or the organic complexing agent is selected in such a manner that, after addition of the ammonia in accordance with step c., a measured hydrodynamic radius of the particles present in the sol in the range from 200 to 2000 nm, preferably 500 to 2000 nm results.