Reversible nanoparticle aggregates and methods for detecting proteases

2:

• The product of manufacture, formulation, mixture or kit of claim 1, wherein the protease is a viral or a mammalian protease.

4:

• The product of manufacture, formulation, mixture or kit of claim 1, wherein the citrate-stabilized NPs is about 20 nm in diameter, or is between about 10 and 50 nm in diameter.

6:

• A solution or formulation comprising the plurality of Arg-Arg-NPs of claim 1(a) and the plurality of Z-PEGx-Y-peptide of claim 1(b), and optionally the solution or formulation comprises a saline solution, water, a cell lysate or a biological solution, and optionally the biological solution comprises a biological fluid from an in vivo source comprises a cell lysate solution, blood, plasma, saliva, urine, bile, a lacrimal duct solution or tear, or cerebrospinal fluid (CSF).

7:

• A method for detecting a protease in a sample, comprising:
• mixing the Arg-Arg-NPs of claim 1(a) and the Z-PEGx-Y-peptide of claim 1(b) in a sample, and presence of a protease capable of specifically recognizing and cleaving the peptide is detected via a proteolytic cleavage that releases Z-PEGx fragments from a Z-PEG-Y-peptide, thus inducing the dissociation of the AuNPs-citrate assemblies and turning the solution from blue to red.

8:

• The method of claim 7, wherein the sample comprises a cell lysate or a biological solution.

9:

• The product of manufacture, formulation, mixture or kit of claim 1, wherein the products formulations or mixtures can aggregate or assemble into nanoparticles such that the nanoparticles undergo plasmonic coupling, and the plasmonic coupling is reversible, or substantially reversible, leading to monodisperse nanoparticles when a chemical cue or signal is added.

10:

• The product of manufacture, formulation, mixture or kit of claim 1, wherein the NP comprises a di-arginine (Arg) citrate-stabilized nanoparticle, or a plurality of di-arginine (Arg) citrate-stabilized nanoparticles (NPs), or Arg-Arg-NPs.

11:

• The product of manufacture, formulation, mixture or kit of claim 1, wherein the Kx-Rx comprises KR, RK, RRK, KRR, RKR, RRKR (SEQ ID NO:4), RKRR (SEQ ID NO:5), KRRR (SEQ ID NO:6), RRRK (SEQ ID NO:7), KKRR (SEQ ID NO:8), KKKR (SEQ ID NO:9), RKKK (SEQ ID NO:10), KRRK (SEQ ID NO:11) or RKKR (SEQ ID NO:12).

12:

• The product of manufacture, formulation, mixture or kit of claim 1, wherein the biological fluid is derived or isolated from an in vivo source.

13:

• The product of manufacture, formulation, mixture or kit of claim 12, wherein the biological fluid is an undiluted and/or untreated biological fluid from an in vivo source.

14:

• The product of manufacture, formulation, mixture or kit of claim 12, wherein the biological fluid from an in vivo source comprises blood, plasma, saliva, urine, bile, a lacrimal duct solution or a tear, or cerebrospinal fluid (CSF);
• a cell lysate;
• or water, distilled water, saline or sea water,

15:

• The product of manufacture, formulation, mixture or kit of claim 1, wherein compound X, or the citrate-stabilized compound X, or the citrate-stabilized nanoparticle (NP) comprises or is conjugated to a metal to generate a metal-nanoparticle or metal-compound X.

16:

• The product of manufacture, formulation, mixture or kit of claim 15, wherein the metal of the metal nanoparticle or metal-compound X comprises silver (Ag) (for example, the nanoparticle comprises Arg-Arg-Ag-NP) or gold (Au) (for example, the nanoparticle comprises Arg-Arg-Au-NP).

18:

• The product of manufacture, formulation, mixture or kit of claim 2, wherein the viral protease is a coronavirus protease.

19:

• The product of manufacture, formulation, mixture or kit of claim 18, wherein the coronavirus protease is a Covid-19 protease or SARS-CoV-2 (Mpro).

20:

• The method of claim 8, wherein the biological solution comprises a biological fluid from an in vivo source comprises a cell lysate solution, blood, plasma, a lacrimal duct solution or (a tear), saliva, urine, bile or cerebrospinal fluid (CSF);
• or the sample comprises water or a saline solution.