D-type amino acid modified gold nanoparticles, and preparation method and application thereof

Abstract

The application relates to the technical field of nanobiological sensing, and discloses D-type amino acid modified gold nanoparticles as well as a preparation method and application thereof, which comprises the following steps: (1) dissolving D-type amino acid in deionized water to obtain a D-type amino acid solution, adding anhydrous acetic acid, a HAuCl4 solution and Tween-80 into the D-type amino acid solution, uniformly mixing, boiling at 100 DEG C, and keeping boiling; under the condition of violent stirring, adding a sodium citrate aqueous solution into the solution prepared in step (1), and continuously keeping boiling; after the reaction is completed, cooling to room temperature; using deionized water to dialyze the solution prepared in step (3), filtering and sterilizing, and obtaining the D-type amino acid modified gold nanoparticles. The D-type amino acid modified gold nanoparticles can detect bacteria through the color change of a solution, realize visual detection of bacteria, and do not need to rely on large instruments.

Description

Technical Field

[0001] This application relates to the field of nanobiosensing technology, and mainly to a D-type amino acid-modified gold nanoparticle, its preparation method and application. Background Technology

[0002] Spontaneous bacterial peritonitis (SBP) caused by ascites is a common cause of death in patients with cirrhosis. A fundamental challenge in the diagnosis and treatment of SBP is the early detection of bacteria in the ascites fluid. Current standard methods for bacterial detection include microbial culture or genetic analysis, both of which require specific environmental conditions. Recent studies have shown that fluorescence imaging or microelectronics can be used for bacterial detection.

[0003] Peptidoglycan (PG) is a major component of bacterial cell walls. N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc) are cross-linked by short peptides to form a peptidoglycan network structure. Given the crucial role of peptidoglycan in cell wall synthesis and bacterial reproduction, researchers have developed numerous antibiotics that inhibit bacterial growth by blocking peptidoglycan synthesis. Furthermore, fluorescence imaging of bacterial surfaces using sugars or oligopeptides has attracted particular attention to reveal the structure of peptidoglycan layers. Due to the relatively poor selectivity of bacterial D,D-transpeptidase, most bacteria can readily utilize exogenous D-amino acids from the surrounding medium to introduce terminal D-alanine residues from the oligopeptide chains on the peptide bridges that link the peptidoglycan layers into their peptidoglycan by substitutional peptides. Given that D-alanyl-D-alanine (DADA) is the tail of peptidoglycan oligopeptides, the attraction between similar molecules and its easy recognition by peptidase make exogenous DADA more readily intercalated into peptidoglycan. Vancomycin can bind bacterial DADA and label peptidoglycan layers by linking it to a fluorescent probe. However, these methods rely on large instruments for labeling and detecting bacteria, making them inconvenient to operate.

[0004] Gold nanoparticles (AuNPs) are widely used in drug delivery carriers, antibacterial agents, photothermal therapy materials, and colorimetric biosensors. Researchers in this field have developed a series of small-molecule modified gold nanoparticles capable of killing multidrug-resistant bacteria. Several colorimetric sensors based on gold nanoparticles have also been reported, which can capture signals with the naked eye without the need for large instruments. Many researchers have reported bacterial biosensors based on gold nanoparticles. Hexadecyltrimethylammonium bromide (CTAB)-coated gold nanoparticles have been studied for bacterial detection; CTAB has a positive charge and can target bacteria with a negatively charged surface. Researchers have also used antibodies or aptamers to decorate AuNPs for bacterial targeting. However, these strategies are easily interfered with by environmental factors such as temperature, pH, metal ions, or proteins. Therefore, there is an urgent need for a stable and simple platform for pathogen detection.

[0005] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this application is to provide a D-amino acid modified gold nanoparticle, its preparation method and application. The D-amino acid modified gold nanoparticle can be used for visual detection of bacteria, aiming to solve the problem that the existing bacterial detection technology requires large equipment and is inconvenient to operate.

[0007] The technical solution of this application is as follows: A method for preparing D-type amino acid-modified gold nanoparticles, comprising the following steps: (1) Dissolve D-type amino acids in deionized water to obtain a D-type amino acid solution. Add anhydrous acetic acid, HAuCl4 solution and Tween-80 to the D-type amino acid solution, mix well, heat to 100°C and boil, and keep boiling. (2) While stirring vigorously, add sodium citrate aqueous solution to the solution prepared in step (1) and continue to boil; (3) After the reaction is complete, cool to room temperature; (4) Dialyze the solution prepared in step (3) with deionized water, filter and sterilize it to obtain the gold nanoparticles modified with the D-type amino acids.

[0008] The method for preparing D-type amino acid-modified gold nanoparticles, wherein in step (1), the concentration of the D-type amino acid solution is 0.01~0.10 mol / L; In step (1), the volume ratio of the anhydrous acetic acid to the D-type amino acid solution is 1:50 to 1:300; In step (1), the molar ratio of HAuCl4 to the D-type amino acid is 1:1 to 1:10; In step (1), the molar ratio of Tween-80 to the D-type amino acid is 1:3 to 1:10; In step (2), the concentration of the sodium citrate aqueous solution is 0.01~0.1mol / L, and the molar ratio of sodium citrate to HAuCl4 is 10:1~3:1.

[0009] The method for preparing D-type amino acid-modified gold nanoparticles, wherein in step (1), the concentration of the D-type amino acid solution is 0.01~0.08 mol / L; In step (1), the volume ratio of the anhydrous acetic acid to the D-type amino acid solution is 1:50 to 1:200; In step (1), the molar ratio of HAuCl4 to the D-type amino acid is 1:1 to 1:5; In step (1), the molar ratio of Tween-80 to the D-type amino acid is 1:4 to 1:8; In step (2), the concentration of the sodium citrate aqueous solution is 0.02~0.08 mol / L, and the molar ratio of sodium citrate to HAuCl4 is 8:1~3:1.

[0010] The method for preparing D-type amino acid-modified gold nanoparticles, wherein in step (1), the concentration of the D-type amino acid solution is 0.02 mol / L; In step (1), the volume ratio of the anhydrous acetic acid to the D-type amino acid solution is 1:100; In step (1), the molar ratio of HAuCl4 to the D-type amino acid is 1:1 to 1:3; In step (1), the molar ratio of Tween-80 to the D-type amino acid is 1:5; In step (2), the concentration of the sodium citrate aqueous solution is 0.05 mol / L, and the molar ratio of sodium citrate to HAuCl4 is 5:1.

[0011] The method for preparing D-type amino acid-modified gold nanoparticles, wherein in step (1), the boiling time is 2 to 20 minutes; In step (2), the stirring speed of the vigorous stirring is 1000~3000 rpm; In step (2), the boiling time is 10 to 40 minutes; In step (3), the cooling process to room temperature is natural cooling; In step (4), the cutoff value for dialysis is 14 kDa MW, and the duration of dialysis is 15 to 36 hours; In step (4), the sterilization method is filtration sterilization.

[0012] The method for preparing D-type amino acid-modified gold nanoparticles, wherein in step (1), the boiling time is 5-15 minutes.

[0013] In step (2), the stirring speed of the vigorous stirring is 1000~2000 rpm; In step (2), the boiling time is 10 to 30 minutes; In step (4), the cutoff value for dialysis is 14 kDa MW, and the dialysis time is 20 to 30 hours; In step (4), the filtration and sterilization process is performed by using a 0.1-0.5 μm filter membrane for filtration and sterilization.

[0014] The method for preparing D-type amino acid-modified gold nanoparticles, wherein in step (1), the boiling time is 10 minutes; In step (2), the stirring speed of the vigorous stirring is 1200 rpm; In step (2), the boiling time is 20 minutes; In step (4), the cutoff value for dialysis is 14 kDa MW, and the duration of dialysis is 24 hours; In step (4), the filtration and sterilization process is performed by using a 0.22 μm filter membrane for filtration and sterilization.

[0015] A D-amino acid-modified gold nanoparticle, wherein it is prepared by the method for preparing D-amino acid-modified gold nanoparticles as described above; The average particle size of the D-type amino acid-modified gold nanoparticles is 1~30 nm.

[0016] The gold nanoparticles modified with D-type amino acids have an average particle size of 3-20 nm.

[0017] An application of the D-amino acid-modified gold nanoparticles as described above, wherein the D-amino acid-modified gold nanoparticles are used for the visual detection of bacteria. The bacteria are one or both of Escherichia coli and Staphylococcus aureus.

[0018] Beneficial effects: The D-amino acid-modified gold nanoparticles of this application can detect bacteria by observing changes in solution color, achieving visual bacterial detection without the need for large instruments. The synthesis method of the D-amino acid-modified gold nanoparticles of this application is simple, the structure is stable, and they are not prone to self-aggregation. The detection process is easy to operate and false positive results are rare, making them a potential bacterial detection reagent. Attached Figure Description

[0019] Figure 1 This is a TEM image of the D-type amino acid-modified gold nanoparticles prepared in Example 1 of this application.

[0020] Figure 2 This is a comparison chart of the experimental results of the control group and the experimental group in Example 2 of this application.

[0021] Figure 3 This is a comparison chart of the stability of Au-DADA prepared in the control example of this application and Au-DADA prepared in Example 1. Detailed Implementation

[0022] This application provides D-type amino acid-modified gold nanoparticles, their preparation method, and applications. To make the objectives, technical solutions, and effects of this application clearer and more explicit, the following provides a more detailed description. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0023] Existing bacterial detection technologies rely on large-scale equipment, which is inconvenient to operate. Gold nanoparticles are widely used in the field of nanobiosensing; however, due to their inherent properties, gold nanoparticles are prone to aggregation, which can lead to false positives. This application provides a method for preparing D-amino acid-modified gold nanoparticles. By optimizing the preparation method, the resulting D-amino acid-modified gold nanoparticles for visual bacterial detection not only enable visual bacterial detection but also reduce the probability of false positives and improve accuracy.

[0024] In this application, D-alanyl-D-alanine is referred to as D-type amino acid or DADA.

[0025] Specifically, the preparation method of D-type amino acid-modified gold nanoparticles of this application includes the following steps: (1) Dissolve D-type amino acids (DADA) in deionized water to obtain a D-type amino acid solution. Add anhydrous acetic acid, chloroauric acid (HAuCl4) solution and Tween-80 to the D-type amino acid solution, mix well, heat to 100℃ and boil, and keep boiling. (2) While stirring vigorously, add sodium citrate aqueous solution to the solution prepared in step (1) and continue to boil; (3) After the reaction is complete, cool to room temperature; (4) Dialyze the solution prepared in step (3) with deionized water, filter and sterilize to obtain gold nanoparticles modified with D-type amino acids (Au-DADA), and store at 4℃.

[0026] In step (1), the concentration of the D-amino acid solution is 0.01~0.10 mol / L, preferably 0.01~0.08 mol / L, and most preferably 0.02 mol / L. Using the preferred concentration can prevent the addition of too much D-amino acid from causing instability of the nanoparticles and avoid incomplete removal of excess D-amino acid during subsequent dialysis. It also prevents the addition of too little D-amino acid from causing uneven and unstable nanoparticle size and agglomeration.

[0027] In step (1), the volume ratio of anhydrous acetic acid to the D-type amino acid solution is 1:50 to 1:300, preferably 1:50 to 1:200, and most preferably 1:100. Adding anhydrous acetic acid activates the D-type amino acids, allowing them to better modify the surface of the nanoparticles. Controlling the amount of anhydrous acetic acid is to prevent insufficient modification of the nanoparticles due to too little anhydrous acetic acid, and also to prevent excessive anhydrous acetic acid from causing incomplete removal of excess acetic acid during subsequent dialysis.

[0028] In step (1), the molar ratio of HAuCl4 to D-type amino acids is 1:1 to 1:10, preferably 1:1 to 1:5, and most preferably 1:1 to 1:3. The ratio is controlled mainly to prevent the nanoparticles from becoming unstable and prone to aggregation due to an excessive amount of chloroauric acid, and also to prevent the removal of D-type amino acids from being incomplete by dialysis in the later stages due to an excessive amount of D-type amino acids.

[0029] In step (1), the boiling time is maintained at 2 to 20 minutes, preferably 5 to 15 minutes, and most preferably 10 minutes. Boiling for 10 minutes helps the various reactants to mix thoroughly and provides a stable reaction environment. If the boiling time is too short, it may lead to uneven mixing of reactants or unstable reaction environment temperature, affecting the synthesis effect; if the boiling time is too long, it wastes synthesis time and causes a small amount of solvent to be consumed, resulting in changes in the environmental concentration.

[0030] Gold nanoparticles modified solely with D-amino acids are prone to uneven particle size and instability, leading to agglomeration. Adding Tween-80, however, can achieve uniform particle size, even dispersion, and reduced agglomeration. Therefore, Tween-80 is also added in this application. The molar ratio of Tween-80 to D-amino acids is 1:3 to 1:10, preferably 1:4 to 1:8, and most preferably 1:5. The amount of Tween-80 needs to be carefully controlled; too much will make it difficult to remove later, while too little will not significantly stabilize the nanoparticles.

[0031] In step (2), the concentration of the sodium citrate aqueous solution is 0.01~0.1 mol / L, preferably 0.02~0.08 mol / L, and most preferably 0.05 mol / L. The molar ratio of sodium citrate to HAuCl4 is 10:1~3:1, preferably 8:1~3:1, and most preferably 5:1.

[0032] In step (2), the stirring speed for vigorous stirring is 1000~3000 rpm, preferably 1000~2000 rpm, and most preferably 1200 rpm.

[0033] In step (2), the boiling time is maintained for 10 to 40 minutes, preferably 10 to 30 minutes, and most preferably 20 minutes. Maintaining boiling for 20 minutes helps the reaction to proceed fully.

[0034] In step (3), the cooling process to room temperature is preferably natural cooling.

[0035] In step (4), the cutoff value for dialysis is 14 kDa MW; the dialysis time is 15-36 hours, preferably 20-30 hours, and most preferably 24 hours. Using these dialysis conditions allows unreacted substances and post-reaction impurities to be dialyzed out, while ensuring that nanoparticles are not dialyzed out. Too short a dialysis time will result in incomplete dialysis, while too long a time will affect the experimental progress.

[0036] In step (4), the filtration and sterilization process involves using a 0.1-0.5 μm filter membrane for filtration and sterilization, with a 0.22 μm filter membrane being the most preferred. Through filtration, a small number of particles with excessively large diameters can be filtered out, while also filtering out any bacteria that may be present, thus achieving the purpose of sterilization.

[0037] This application also provides D-amino acid-modified gold nanoparticles, which are prepared by the above-described preparation method. The average particle size of the D-amino acid-modified gold nanoparticles is 1-30 nm, preferably 3-20 nm.

[0038] This application also provides an application of D-amino acid-modified gold nanoparticles for the visual detection of bacteria. Specifically, the bacteria can be one or both of Escherichia coli and Staphylococcus aureus.

[0039] The D-amino acid-modified gold nanoparticles of this application have the following beneficial effects: 1. The D-amino acid-modified gold nanoparticles of this application can detect bacteria by observing changes in solution color, achieving visual bacterial detection without the need for large instruments. The D-amino acid-modified gold nanoparticles prepared in this application are in a solution state and appear wine-red. When the sample to be tested contains bacteria, the D-amino acid-modified gold nanoparticles aggregate on the bacteria via DADA, causing the D-amino acid-modified gold nanoparticles to aggregate and resulting in a change in the solution from wine-red to purplish-red or bluish-purple.

[0040] 2. The synthesis method of the D-type amino acid modified gold nanoparticles of this application is simple, the structure is stable, it is not easy to self-aggregate, the detection process is easy to operate, and false positive results are not likely to occur. It is a potential bacterial detection reagent.

[0041] The present application will be further described below through specific embodiments.

[0042] Example 1: This example illustrates the synthesis of D-amino acid-modified gold nanoparticles (Au-DADA).

[0043] D-amino acid (DADA) (16 mg, 0.1 mmol) was dissolved in 5 mL of deionized water. 50 μL of anhydrous acetic acid and HAuCl4 solution (20 mg, 0.05 mmol, dissolved in 0.4 mL of deionized water) and Tween-80 (8.58 mg, 0.02 mmol) were added and mixed thoroughly. The solution was heated to 100 °C and boiled for 10 minutes. Sodium citrate aqueous solution (10 mg, 0.05 mmol, dissolved in 1 mL of deionized water) was added dropwise with vigorous stirring (1200 rpm). The solution gradually changed from pale yellow to wine red, and boiling was continued for another 20 minutes. The solution was then dialyzed against deionized water (14 kDa MW cutoff, Millipore) for 24 hours, filtered, sterilized through a 0.22 μm filter (Millipore), and stored at 4 °C.

[0044] Figure 1 This is a TEM image of the D-amino acid-modified gold nanoparticles prepared in Example 1. The nanoparticle size is as shown in the image. Figure 1 As shown, the particle size is approximately 10~25nm, and the particle size is uniform with good dispersibility.

[0045] Example 2: This embodiment illustrates the visualization detection of bacteria using D-amino acid-modified gold nanoparticles.

[0046] Preparation of bacterial culture: Staphylococcus aureus was cultured in LB broth to a concentration of 1.0 × 10⁻⁶. 8CFU / mL, then diluted to 1.0 × 10⁻⁶. 6 Staphylococcus aureus solution was prepared using CFU / mL. Escherichia coli solution was prepared using the same method.

[0047] Preparation of gold nanoparticle culture medium solution: LB culture medium and Au-DADA prepared in Example 1 were mixed at a volume ratio of 1:1.

[0048] Bacterial assays were performed in 96-well microplates (Constar, 3599).

[0049] Experimental group: First, 90 μL of gold nanoparticles diluted with LB medium was added to a 96-well microplate to obtain a gold nanoparticle culture medium solution. Then, 10 μL of the prepared bacterial suspension was added to the gold nanoparticle culture medium solution (final bacterial concentration: 1.0 × 10⁻⁶). 5 (CFU / mL), one well contains Staphylococcus aureus and the other well contains Escherichia coli.

[0050] Control group: 100 μL of gold nanoparticle culture medium solution was added as the control group.

[0051] The 96-well microculture plate was incubated at 37°C for 1 hour, and then the color change was observed. The results are as follows. Figure 2 As shown. In Figure 2 In the diagram, the top row of wells represents the control group (labeled "Au-DADA"), and the bottom row represents the experimental groups (labeled "Au-DADA & Staphylococcus aureus" and "Au-DADA & Escherichia coli"). From... Figure 2 As can be seen, the culture wells in the control group remained wine-red, while the culture wells in the experimental group turned purplish-blue. This indicates that when the sample contains Escherichia coli or Staphylococcus aureus, the liquid color will change. The presence of bacteria can be determined by the change in solution color.

[0052] Comparison Example The preparation method of the gold nanoparticles (Au-DADA) in this comparative example is the same as that in Example 1, except that Tween-80 was not added in the comparative example.

[0053] Dilute 1 mL of the Au-DADA solution prepared in the control example with 1 mL of LB medium. Add 100 μL of the diluted Au-DADA solution to a 96-well microplate. The liquid will be wine-red in color at this point. Figure 3As shown (the second well in the first row and column is the pre-culture control Au-DADA). Dilute 1 mL of Au-DADA prepared in Example 1 with 1 mL of LB medium. Add 100 μL of the diluted Au-DADA solution from Example 1 to a 96-well microplate; the liquid will be wine-red at this point. Figure 3 As shown (the first well in the first row and column is the Au-DADA of Example 1 before cultivation).

[0054] The 96-well microplate was incubated at 37°C for 1 hour, and then the color change was observed. After incubation, the solution in the wells containing the control Au-DADA solution turned a light purplish-red color, such as... Figure 3 As shown (the second well in the second row and column is the control example Au-DADA after cultivation). The solution in the wells containing the Au-DADA solution from Example 1 remained red, with no significant color change. Figure 3 As shown (the first well in the second row and column is the Au-DADA of Example 1 before cultivation).

[0055] It should be understood that the application of this application is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of this application.

Claims

1. A method for preparing D-type amino acid-modified gold nanoparticles, characterized in that, Includes the following steps: (1) Dissolve D-type amino acids in deionized water to obtain a D-type amino acid solution. Add anhydrous acetic acid, HAuCl4 solution and Tween-80 to the D-type amino acid solution, mix well, heat to 100°C and boil, and keep boiling. (2) While stirring vigorously, add sodium citrate aqueous solution to the solution prepared in step (1) and continue to boil; (3) After the reaction is complete, cool to room temperature; (4) Dialyze the solution prepared in step (3) with deionized water, filter and sterilize it to obtain the gold nanoparticles modified with the D-type amino acids.

2. The method for preparing D-type amino acid-modified gold nanoparticles according to claim 1, characterized in that, In step (1), the concentration of the D-type amino acid solution is 0.01~0.10 mol / L; In step (1), the volume ratio of the anhydrous acetic acid to the D-type amino acid solution is 1:50 to 1:300; In step (1), the molar ratio of HAuCl4 to the D-type amino acid is 1:1 to 1:10; In step (1), the molar ratio of Tween-80 to the D-type amino acid is 1:3 to 1:10; In step (2), the concentration of the sodium citrate aqueous solution is 0.01~0.1mol / L, and the molar ratio of sodium citrate to HAuCl4 is 10:1~3:

1.

3. The method for preparing D-type amino acid-modified gold nanoparticles according to claim 1, characterized in that, In step (1), the concentration of the D-type amino acid solution is 0.01~0.08 mol / L; In step (1), the volume ratio of the anhydrous acetic acid to the D-type amino acid solution is 1:50 to 1:200; In step (1), the molar ratio of HAuCl4 to the D-type amino acid is 1:1 to 1:5; In step (1), the molar ratio of Tween-80 to the D-type amino acid is 1:4 to 1:8; In step (2), the concentration of the sodium citrate aqueous solution is 0.02~0.08 mol / L, and the molar ratio of sodium citrate to HAuCl4 is 8:1~3:

1.

4. The method for preparing D-type amino acid-modified gold nanoparticles according to claim 1, characterized in that, In step (1), the concentration of the D-type amino acid solution is 0.02 mol / L; In step (1), the volume ratio of the anhydrous acetic acid to the D-type amino acid solution is 1:100; In step (1), the molar ratio of HAuCl4 to the D-type amino acid is 1:1 to 1:3; In step (1), the molar ratio of Tween-80 to the D-type amino acid is 1:5; In step (2), the concentration of the sodium citrate aqueous solution is 0.05 mol / L, and the molar ratio of sodium citrate to HAuCl4 is 5:

1.

5. The method for preparing D-type amino acid-modified gold nanoparticles according to claim 1, characterized in that, In step (1), the boiling time is 2 to 20 minutes; In step (2), the stirring speed of the vigorous stirring is 1000~3000 rpm; In step (2), the boiling time is 10 to 40 minutes; In step (3), the cooling process to room temperature is natural cooling; In step (4), the cutoff value for dialysis is 14 kDa MW, and the duration of dialysis is 15 to 36 hours; In step (4), the sterilization method is filtration sterilization.

6. The method for preparing D-type amino acid-modified gold nanoparticles according to claim 1, characterized in that, In step (1), the boiling time is 5 to 15 minutes; In step (2), the stirring speed of the vigorous stirring is 1000~2000 rpm; In step (2), the boiling time is 10 to 30 minutes; In step (4), the cutoff value for dialysis is 14 kDa MW, and the dialysis time is 20 to 30 hours; In step (4), the filtration and sterilization process is performed by using a 0.1-0.5 μm filter membrane for filtration and sterilization.

7. The method for preparing D-type amino acid-modified gold nanoparticles according to claim 1, characterized in that, In step (1), the boiling time is 10 minutes; In step (2), the stirring speed of the vigorous stirring is 1200 rpm; In step (2), the boiling time is 20 minutes; In step (4), the cutoff value for dialysis is 14 kDa MW, and the duration of dialysis is 24 hours; In step (4), the filtration and sterilization process is performed by using a 0.22 μm filter membrane for filtration and sterilization.

8. A type D amino acid-modified gold nanoparticle, characterized in that, The gold nanoparticles were prepared using the method for preparing D-type amino acid-modified gold nanoparticles as described in any one of claims 1-7. The average particle size of the D-type amino acid-modified gold nanoparticles is 1~30 nm.

9. The D-amino acid-modified gold nanoparticles according to claim 8, characterized in that, The average particle size of the D-type amino acid-modified gold nanoparticles is 3~20 nm.

10. An application of the D-amino acid-modified gold nanoparticles as described in any one of claims 8-9, characterized in that, The D-amino acid-modified gold nanoparticles were used for the visual detection of bacteria. The bacteria are one or both of Escherichia coli and Staphylococcus aureus.

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