The biomimetic synthesis of relevant silica materials using biological macromolecules as templates via silica biomineralization processes attract rapidly rising attention toward natural and artificial materials. Biomimetic synthesis studies are useful for improving the understanding of the formation mechanism of the hierarchical structures found in living organisms (such as diatoms and sponges) and for promoting significant developments in the biotechnology, nanotechnology and materials chemistry fields. Chirality is a ubiquitous phenomenon in nature and is an inherent feature of biomolecular components in organisms. Helical biomolecules, one of the most important types of chiral macromolecules, can self-assemble into multiple liquid-crystal structures and be used as biotemplates for silica biomineralization, which renders them particularly useful for fabricating complex silica materials under ambient conditions. Over the past two decades, many new silica materials with hierarchical structures and complex morphologies have been created using helical biomolecules. In this review, the developments in this field are described and the recent progress in silica biomineralization templating using several classes of helical biomolecules, including DNA, polypeptides, cellulose and rod-like viruses is summarized. Particular focus is placed on the formation mechanism of biomolecule–silica materials (BSMs) with hierarchical structures. Finally, current research challenges and future developments are discussed in the conclusion.

With different scales of chirality, chiral materials have various particular properties and potential applications in many fields. Peptides are the fundamental building units of biological systems, and a variety of ordered functional nanostructures are produced through self-assembly and biomineralization of peptides in nature. This Personal Account describes chiral silica materials fabricated by using amphiphilic peptides as building blocks. Three particular biomineralization approaches are described based on different kinds of geometry of amphiphilic peptides: the influence of the specific amino acid proline in the peptide sequence, the hydrophilicity of amphiphilic peptides, and different kinds of hydrophobic tails in amphiphilic peptides. These strategies are useful for designing peptides toward the bottom-up synthesis of nanomaterials as well as improving the understanding of the mechanism of peptide self-assembly.

Inorganic nanomaterials endowed with hierarchical chirality could open new horizons in physical theory and applications because of their fascinating properties. Here, we report chiral ZnO films coated on quartz substrates with a hierarchical nanostructure ranging from atomic to micrometer scale. Three levels of hierarchical chirality exist in the ZnO films: helical ZnO crystalline structures that form primary helically coiled nanoplates, secondary helical stacking of these nanoplates, and tertiary nanoscale circinate aggregates formed by several stacked nanoplates. These films exhibited optical activity (OA) at 380 nm and in the range of 200–800 nm and created circularly polarized luminescence centered at 510 nm and Raman OA at 50–1400 cm⁻¹, which was attributed to electronic transitions, scattering, photoluminescent emission, and Raman scattering in a dissymmetric electric field. The unprecedented strong OA could be attributed to multiple light scattering and absorption-enhanced light harvesting in the hierarchical structures.

Inorganic nanomaterials endowed with hierarchical chirality could open new horizons in physical theory and applications because of their fascinating properties. Here, we report chiral ZnO films coated on quartz substrates with a hierarchical nanostructure ranging from atomic to micrometer scale. Three levels of hierarchical chirality exist in the ZnO films: helical ZnO crystalline structures that form primary helically coiled nanoplates, secondary helical stacking of these nanoplates, and tertiary nanoscale circinate aggregates formed by several stacked nanoplates. These films exhibited optical activity (OA) at 380 nm and in the range of 200–800 nm and created circularly polarized luminescence centered at 510 nm and Raman OA at 50–1400 cm⁻¹, which was attributed to electronic transitions, scattering, photoluminescent emission, and Raman scattering in a dissymmetric electric field. The unprecedented strong OA could be attributed to multiple light scattering and absorption-enhanced light harvesting in the hierarchical structures.

Peptides, the fundamental building units of biological systems, are chiral in molecular scale as well as in spatial conformation. Shells are exquisite examples of well-defined chiral structures produced by natural biomineralization. However, the fundamental mechanism of chirality expressed in biological organisms remains unclear. Here, we present a system that mimics natural biomineralization and produces enantiopure chiral inorganic materials with controllable helicity. By tuning the hydrophilicity of the amphiphilic peptides, the chiral morphologies and mesostructures can be changed. With decreasing hydrophilicity of the amphiphilic peptides, we observed that the nanostructures changed from twisted nanofibers with a hexagonal mesostructure to twisted nanoribbons with a lamellar mesostructure, and the extent of the helicity decreased. Defining the mechanism of chiral inorganic materials formed from peptides by noncovalent interactions can improve strategies toward the bottom-up synthesis of nanomaterials as well as in the field of bioengineering.

In nature, diatoms and sponges are exquisite examples of well-defined structures produced by silica biomineralisation, in which proteins play an important role. However, the artificial peptide templating route for the silica mesostructure remains a formidable and unsolved challenge. Herein, we report our effort on the design of amphiphilic peptides for synthesising a highly ordered two-dimensional (2D)-hexagonal and lamellar chiral silica mesostructure using trimethoxysilylpropyl-N,N,N-trimethylammonium chloride as the co-structure directing agent (CSDA). The geometry of the peptide was designed by adding proline residues into the hydrophobic chain of the peptide to break the β-sheet conformation by weakening the intermolecular hydrogen bonds; this led to the mesophase transformation from the most general lamellar structure to the 2D hexagonal P6mm mesostructure by increasing the amphiphilic molecules packing parameter g. Enantiomerically pure chiral mesostructures were formed thanks to the intrinsic chirality and relatively strong intermolecular hydrogen bonds of peptides.

Chirality is widely found in nature and is expressed hierarchically in many organic–inorganic hybrid materials. Optical activity (OA) is the most fundamental attribute of these chiral materials. In this study, we found that the OA of impeller-like chiral DNA–silica assemblies (CDSAs) was inverted with the addition of water. The state of DNA under dry and wet conditions, and the dual chirality of chiral DNA layers and twisted helical arrays of opposite handedness in CDSAs were considered to exert predominant effects on the OAs. The circular dichroism (CD) responses for the dry CDSAs were mostly attributed to the chiral arrangement of DNA layers, whereas the opposite CD responses for the wet CDSAs primarily originated from twisted helical arrays of DNA molecules. The observed CD signals were a super-position of the two opposing OA responses. The increase in the longitudinal relation of DNA molecules due to the recovery of a double-helical structure of DNA in the presence of water was considered to be the reason for the increase in intensity of the CD signals that originated from the twisted helical array, which led to the inversion of OA of the CDSAs. The inversion of the plasmon-resonance-based OAs for the chiral-arranged achiral Ag nanoparticles (NPs) located in the channels of the CDSAs in dry and wet states further confirmed the dual chirality of DNA packing. Such research on DNA assemblies and metal NPs with dual, opposite chirality assists in the understanding of DNA hierarchical chirality in living systems and the creation of macroscopic ordered helical materials and biosensors.

Chiroptical properties of pure inorganic material have been achieved by dispersing small amounts of achiral Ag nanoparticles into highly ordered chiral mesoporous silica. There are three types of chirality in chiral mesoporous silica: i) the helical hexagonal surface, ii) the helical pore orientation, and iii) the helical arrangement of aminopropyl groups on the surface of the mesopores, all of which impart plasmonic circular dichroism and have been investigated by introducing Ag nanoparticles into the as-made, calcined and extracted chiral mesoporous silica, respectively. The three types of optical response originate from asymmetric plasmon-plasmon interactions of achiral Ag nanoparticles in three types of chiral environments. Among the three sources of chirality, the helical pore orientation was considered to be predominantly responsible for the optical response owing to the high efficiency of nanoscale chirality. Interestingly, large Ag nanoparticles aggregation as a result of calcination still resulted in a strong optical activity, even the chiral mesostructure was destroyed completely. Rather than the pitch length, the length of helical channel was more effective for increasing the intensity of plasmonic circular dichroism due to longitudinal propagation of Ag nanoparticles along helical channel. Such novel chiral inorganic material will bring new opportunities in non-linear optics, biosensors and chiral recognition.

Two-dimensional (2D) anisotropic silver nanowire (AgNW) arrays, fabricated inside chiral mesoporous silica (CMS), exhibited strong and tunable plasmon circular dichroism (CD) signals in the visible and near-IR regions due to collective dipole coupling between the anisotropic AgNWs. The multihelix with a helical channel orientation and helical arrays of opposite handedness in CMS played a predominant effects on the transversal and longitudinal chirality of the AgNWs, respectively.This behavior differs from both isotropic-nanoparticle and single-helix-induced CD responses. This system will provide new insight into the optical activity of metal inorganic nanoparticles capped with chiral organic molecules and assembled in chiral environments.

Antipodal twisted helical ribbons with lamellar bilayer structure were obtained by self-assembly of chiral amphiphilic molecules in water and water/ethanol. The handedness inversion of the molecular arrangement in these antipodal helical ribbons was investigated by using chiroptical spectroscopy and molecular probes in their antipodal mesoporous silica assemblies synthesized through pairing interaction between the head group of the chiral amphiphilic molecules and a co-structure-directing agent. The supramolecular chirality is imprinted in the pore surface through the organic group of the co-structure-directing agent. The mirror-image diffuse-reflectance circular dichroism spectra of the conjugated discotic probing molecule introduced into their supramolecular chiral imprinted mesoporous silica demonstrated the origin of inverse chirality from the antipodal helical stacking of the molecules.

The physical or chemical event that generally causes stimuli responses is limited to the formation or destruction of secondary forces, such as hydrogen bonding, hydrophobic effects, electrostatic interactions, and simple reactions. Here, pH-responsive behavior of metal–organic coordination bonding, which is intrinsic to natural systems (e.g., transferrin recycling in cells), is becoming a strong candidate for a new stimulus–responsive route. We have designed a simple pH-responsive release system by integrating a metal ion and ligand or self-assembling these species with biodegradable host molecules to form nanoparticles with “metal–ligand” or “host–metal–ligand” architectures. The cleavage of either or both the “metal–ligand” or the “host–metal” coordination bond in response to pH variations causes significant damage to the nanoparticles and the subsequent release of ligand molecules under designated pH conditions.

This article provides a brief overview of functional mesoporous silica materials synthesized by the co-structure-directing route, which is distinct from conventional synthesis strategies. In these systems, organosilane serves as the co-structure-directing agent (CSDA), which provides critical interactions between the template and organic part of the organosilane to form mesostructures, thus retaining the organic groups on the pore surface after removal of the template by extraction. i) The formation of anionic-surfactant-templated mesoporous silicas (AMSs) has been achieved by the co-structure-directing route, which leads to a variety of mesostructures, porous properties and morphologies. ii) Other co-structure-directing systems for synthesizing mesoporous silicas have also been achieved, including systems using cationic surfactants and non-surfactants, and systems using DNA for constructing nanofibers and DNA–silica liquid crystalline complexes. iii) Evidence for the regular arrangement of functional groups on the pore surface resulted from the co-structure-directing effect has been discussed. Also included is a brief description of the application, future requirements, and trends in the development of mesoporous materials by the co-structure-directing route.

Hierarchical silica nanotubes with radially oriented mesoporous channels perpendicular to the central axis of the tube were synthesized by using self-assembled chiral anionic surfactant, co-structure directing agent (CSDA) and silica precursor. The average inner diameter and the wall thickness were ∼94, ∼62, and ∼62 nm and to ∼27, ∼33, and ∼45 nm, respectively, by manipulating the synthesis gel composition, while the diameter of the wall mesopores was kept constant at ∼4 nm. These materials with such a unique structure were produced only with chiral surfactant and achiral or racemic surfactant did not give rise to mesoporous silica nanotubes. The existence of helicity in the lipid bilayer template was confirmed by means of circular dichroism spectroscopy. The mesoporous penetrating from outside to inside of silica nanotubes are thought to originate from the initial formation of self-assembled lipid tubes with helical bilayers, which in turn re-assemble to form the mesopores in the wall of the nanotubes upon addition of co-structure directing agent and silica source.

Conducting polymer nanofibers with controllable chiral mesopores in the size, the shape, and handedness have been synthesized by chiral lipid ribbon templating and “seeding” route. Chiral mesoporous conducting poly(pyrrole) (CMPP) synthesized with very small amount of chiral amphiphilic molecules (usually < 3%) has helically twisted channels with well-defined controllable pore size of 5–20 nm in central axis of the twisted fibers. The structure and chirality of helical mesopores have been characterized by high-resolution transmission electron microscope (HRTEM), scanning electron microscope (SEM) and electron tomography. The average pore diameters of chiral mesopores were approximately estimated from the N₂ adsorption–desorption data and calculated by the conversion calculation from helical ribbons to a rectangular straight tape. The pore size of CMPP has been controlled by choosing different alkyl chain lengths of chiral lipid molecules or precisely adjusting the H₂O/EtOH volume ratio.

The synthesis system for mesophase formation, using the diprotic anionic surfactant N-myristoyl-L-glutamic acid (C₁₄GluA) as the structure-directing agent (SDA) and N-trimethoxylsilylpropyl-N,N,N-trimethylammonium chloride (TMAPS) as the co-structure-directing agent (CSDA), has been investigated and a full-scaled synthesis-field diagram is presented. In this system we have obtained mesophases including three-dimensional (3D) micellar cubic Fmm, Pmn, Fdm, micellar tetragonal P4₂/mnm, two-dimensional (2D) hexagonal p6mm and bicontinuous cubic Pnm, by varying the C₁₄GluA/NaOH/TMAPS composition ratios. From the diagram it can be concluded that the mesophase formation is affected to a high degree by the organic/inorganic-interface curvature and the mesocage–mesocage electrostatic interaction. Bicontinuous cubic and 2D-hexagonal phases were found in the low organic/inorganic-interface curvature zones, whereas micellar cubic and tetragonal mesophases were found in the high organic/inorganic-interface curvature zones. Formation of cubic Fmm and tetragonal P4₂/mnm was favoured in highly alkaline zones with strong mesocage–mesocage interactions, and formation of cubic Pmn and Fdm was favoured with moderate mesocage–mesocage interactions in the less alkaline zones of the diagram.

Using lipids (N-acyl amino acids) and 3-aminopropyltriethoxysilane as structure- and co-structure-directing agents, mesoporous silicas with four different morphologies, that is, helical ribbon (HR), hollow sphere, circular disk, and helical hexagonal rod, were synthesized just by changing the synthesis temperature from 0 °C to 10, 15, or 20 °C. The structures were studied by electron microscopy. It was found that 1) the structures have double-layer disordered mesopores in the HR, radially oriented mesopores in the hollow sphere, and highly ordered straight and chiral 2D-hexagonal mesopores in the disklike structure and helical rod, respectively; 2) these four types of mesoporous silica were transformed from the flat bilayered lipid ribbon with a chain-interdigitated layer phase through a solid–solid transformation for HR formation and a dissolving procedure transformation for the synthesis of the hollow sphere, circular disk, and twisted morphologies; 3) the mesoporous silica helical ribbon was exclusively right-handed and the 2D-hexagonal chiral mesoporous silica was excessively left-handed when the L-form N-acyl amino acid was used as the lipid template; 4) the HR was formed only by the chiral lipid molecules, whereas the 2D-hexagonal chiral mesoporous silicas were formed by chiral, achiral, and racemic lipids. Our findings give important information for the understanding of the formation of chiral materials at the molecular level and will facilitate a more efficient and systematic approach to the generation of rationalized chiral libraries.